I'm gradually becoming seduced by the idea of CNC on a mill. The 
question is whether to convert my Tom Senior M1 to CNC, or whether to 
buy a KX1 or a KX3 - to be honest I like the idea of a new toy!

Some questions:
- Has anyone here got any opinions on the KX1 or KX3 compared to an M1?

- Has anyone in the South got a KX1 or KX3 running that I could have a 
look at (within striking-range of Winchester)?

- How easy/hard is it to convert an M1 to CNC? (I'll ask in the TS 
owner's group too)

- Never having used CNC before, if I bought a KX3 would I want to keep 
the M1 for manual work or is it reasonable to plan to do everything with 
CNC?

Dave

On 3 Aug, 12:30, NoSpam  wrote:
> I'm gradually becoming seduced by the idea of CNC on a mill. The
> question is whether to convert my Tom Senior M1 to CNC, or whether to
> buy a KX1 or a KX3 - to be honest I like the idea of a new toy!
>
> Some questions:
> - Has anyone here got any opinions on the KX1 or KX3 compared to an M1?
>
> - Has anyone in the South got a KX1 or KX3 running that I could have a
> look at (within striking-range of Winchester)?
>
> - How easy/hard is it to convert an M1 to CNC? (I'll ask in the TS
> owner's group too)
>
> - Never having used CNC before, if I bought a KX3 would I want to keep
> the M1 for manual work or is it reasonable to plan to do everything with
> CNC?
>
> Dave

First off, YMMV, however...

I decided to go down the "convert a decent old fashioned mill" route
for several reasons, I know I'm starting with a quality machine, I
know I can spec EVERY single component to my own desires, and perhaps
most of all because I think that having done a conversion I will be
more able to understand and therefore use the thing properly...

I also think it works out a lot cheaper, cost per quality wise.

Motion Control Products for your steppers and drivers
http://video.google.com/videoplay?docid=-7470965926215097427&hl=en

The rest of it you can make easy enough, but if you'd rather buy then
Reliance Precision Mechatronics for things like couplings and belts
and pulleys and ballscrews....

I tell you one HUGE benefit, you already know by sound and feel and
all that good stuff how all your tooling and your mill sounds when
things are optimal and when they are not, you get all that for free
when doing a conversion.

Any questions ask away, or if you're in the southwest you can always
drop by and nose around.

Cost wise I can convert both the mill and lathe to CNC for less than
400 quid all in, and that is all quality branded industrial products
made to spec, no fleabay stuff, no chinese stuff, none of that.

plus, a bit more detail and thoughts... scuse the mess...

http://video.google.com/videoplay?docid=-8046410346841899515&hl=en

Guy Fawkes wrote:
> plus, a bit more detail and thoughts... scuse the mess...
> 
> http://video.google.com/videoplay?docid=-8046410346841899515&hl=en

Very interesting video,  thanks for posting that.

-- 
Boo

>On 3 Aug, 13:48, Guy Fawkes  wrote:

>
> Cost wise I can convert both the mill and lathe to CNC for less than
> 400 quid all in, and that is all quality branded industrial products
> made to spec, no fleabay stuff, no chinese stuff, none of that.

One point to note is that Motion Control products sell Leadshine
drives and steppers from China.
These are the same drives and steppers that Arc sells but at a higher
price.

John S.

Guy Fawkes wrote:
> plus, a bit more detail and thoughts... scuse the mess...
> 
> http://video.google.com/videoplay?docid=-8046410346841899515&hl=en

Thanks for that - 'very interesting!
Could you go into a little detail about the steppers and controllers 
that you've used (choice, types, suppliers, etc)?

Dave

NoSpam wrote:
> Guy Fawkes wrote:
>> plus, a bit more detail and thoughts... scuse the mess...
>>
>> http://video.google.com/videoplay?docid=-8046410346841899515&hl=en
> 
> Thanks for that - 'very interesting!
> Could you go into a little detail about the steppers and controllers 
> that you've used (choice, types, suppliers, etc)?
> 
> Dave

Oops sorry, just watched the earlier vid. and all the info is already there.

On 3 Aug, 21:34, John S  wrote:
> >On 3 Aug, 13:48, Guy Fawkes  wrote:
>
> > Cost wise I can convert both the mill and lathe to CNC for less than
> > 400 quid all in, and that is all quality branded industrial products
> > made to spec, no fleabay stuff, no chinese stuff, none of that.
>
> One point to note is that Motion Control products sell Leadshine
> drives and steppers from China.
> These are the same drives and steppers that Arc sells but at a higher
> price.
>
> John S.

When I was initially researching this I asked arc for a graph of
stepper torque vs rpm, they couldn't help, I rang MCP and spoke to the
bod there and he just rattled it all off, plus they had a far greater
range, plus I found that they were actually cheaper than arc or anyone
else, most of all my decision was based on the fact that MCP don't do
anything but steppers and servos, YMMV

http://www.motioncontrolproducts.co.uk/index.php

On 3 Aug, 23:11, Guy Fawkes  wrote:

> When I was initially researching this I asked arc for a graph of
> stepper torque vs rpm, they couldn't help, I rang MCP and spoke to the
> bod there and he just rattled it all off, plus they had a far greater
> range, plus I found that they were actually cheaper than arc or anyone
> else, most of all my decision was based on the fact that MCP don't do
> anything but steppers and servos, YMMV
>
> http://www.motioncontrolproducts.co.uk/index.php

Just checked and on the smaller drive MCP don't have the same as Arc,
theirs is 2.5 amp at £24.10  vat = £28.31
Arc's is 3 amp at £28.95 including
On the larger drive, again both Leadshine drives from China
MCP is £70.66  vat = 83.03
Arc is £67.00 inclusive.

I only know this as I have just had a machine and some bits delivered
for a conversion and the customer was going to go to MCP but went to
arc instead and saved himself £64 just on the drivers.

John S.

On 3 Aug, 23:26, John S  wrote:
> On 3 Aug, 23:11, Guy Fawkes  wrote:
>
> > When I was initially researching this I asked arc for a graph of
> > stepper torque vs rpm, they couldn't help, I rang MCP and spoke to the
> > bod there and he just rattled it all off, plus they had a far greater
> > range, plus I found that they were actually cheaper than arc or anyone
> > else, most of all my decision was based on the fact that MCP don't do
> > anything but steppers and servos, YMMV
>
> >http://www.motioncontrolproducts.co.uk/index.php
>
> Just checked and on the smaller drive MCP don't have the same as Arc,
> theirs is 2.5 amp at £24.10  vat = £28.31
> Arc's is 3 amp at £28.95 including
> On the larger drive, again both Leadshine drives from China
> MCP is £70.66  vat = 83.03
> Arc is £67.00 inclusive.
>
> I only know this as I have just had a machine and some bits delivered
> for a conversion and the customer was going to go to MCP but went to
> arc instead and saved himself £64 just on the drivers.
>
> John S.

Look at the two pdf's

http://www.arceurotrade.co.uk/projects/stepper/7A%20Bipolar%20Stepper%20Motor%20Controller%20SMD1478250.pdf

and

http://www.motioncontrolproducts.co.uk/redirect.php?action=url&goto=www.motioncontrolproducts.co.uk%2Fpdf%2FMSD980datasheet.pdf

These are NOT identical, the MCP one will tolerate higher supply
voltages and lower signal powers.

there are many such differences, plus, like I said, when I spoke to E
at MCP I was quoted a price better than shown on the web and better
tham arc, who didn't stock 3nm motors, psu or breakouts when I was
looking, paid by plastic and it all arrived the next day.

I really do NOT want to be putting words in anyones mouths or
denigrating one supplier with respect to another here, but I think
this is a lot like TFT screens and CPU dies, you can grade each
production batch differently, but the deal maker for me was being able
to speak to a specialist firm and a very knowledgeable employee who
knew the subject and could answer everything I asked with ease, so for
example I'd rather buy a laser centre finder direct from the maker in
the states than from chronos here.

On 3 Aug, 23:47, Guy Fawkes  wrote:
> On 3 Aug, 23:26, John S  wrote:
>
>
>
> > On 3 Aug, 23:11, Guy Fawkes  wrote:
>
> > > When I was initially researching this I asked arc for a graph of
> > > stepper torque vs rpm, they couldn't help, I rang MCP and spoke to the
> > > bod there and he just rattled it all off, plus they had a far greater
> > > range, plus I found that they were actually cheaper than arc or anyone
> > > else, most of all my decision was based on the fact that MCP don't do
> > > anything but steppers and servos, YMMV
>
> > >http://www.motioncontrolproducts.co.uk/index.php
>
> > Just checked and on the smaller drive MCP don't have the same as Arc,
> > theirs is 2.5 amp at £24.10  vat = £28.31
> > Arc's is 3 amp at £28.95 including
> > On the larger drive, again both Leadshine drives from China
> > MCP is £70.66  vat = 83.03
> > Arc is £67.00 inclusive.
>
> > I only know this as I have just had a machine and some bits delivered
> > for a conversion and the customer was going to go to MCP but went to
> > arc instead and saved himself £64 just on the drivers.
>
> > John S.
>
> Look at the two pdf's
>
> http://www.arceurotrade.co.uk/projects/stepper/7A%20Bipolar%20Stepper...
>
> and
>
> http://www.motioncontrolproducts.co.uk/redirect.php?action=url&goto=w> These are NOT identical, the MCP one will tolerate higher supply
> voltages and lower signal powers.
>

I'll let you into a small secret, regardless of what's printed on the
data sheets BOTH these drivers carry the same Leadshine part number
and come from the same factory.
The MCP ones state 68 volts typical, which is where the Arc ones will
be at 80 volts with some headroom.
Signal power is also roughly the same 10 ma compared to 12 ma because
they are the same driver.
Who's worried about 2 ma signal power anyway? a decent breakout board
will take care of that.

I also do not want to be putting words in anyones mouths or
denigrating one supplier with respect to another here but just point
out that both products ARE the same.
It's then up to the individual to deal with whoever they want.

John S.

John S.

Guy Fawkes wrote:

> The rest of it you can make easy enough, but if you'd rather buy then
> Reliance Precision Mechatronics for things like couplings and belts
> and pulleys and ballscrews....

Afaict Reliance don't sell ballscrews, just (expensive) leadscrews?

(looking for some cheaper ballscrews, any ideas)

-- Peter Fairbrother

On 4 Aug, 07:55, Peter Fairbrother  wrote:
> Guy Fawkes wrote:
> > The rest of it you can make easy enough, but if you'd rather buy then
> > Reliance Precision Mechatronics for things like couplings and belts
> > and pulleys and ballscrews....
>
> Afaict Reliance don't sell ballscrews, just (expensive) leadscrews?
>
> (looking for some cheaper ballscrews, any ideas)
>
> -- Peter Fairbrother

Couplings or HTD belt pulleys can be bought cheaper believe it or not
from RS Components, they can beat anyone else hands down, I know they
can be expensive on some items but on these that are good.

Cheap ballscrews can be bought from Moore.
http://www.moore-international.com/

Watch the accuracy though as to where you buy.
This 0.003" per foot for some companies means it WILL be out 0.003"
per foot, some like NSK or the other big makes will list this as a
worst case.

So buying a class 5 from a cheap supplier will mean it's a class 5,
from THK or NSK, chances are you will get close to a class 3.

John S.

Guy Fawkes wrote:
> Look at the two pdf's
> 
> http://www.arceurotrade.co.uk/projects/stepper/7A%20Bipolar%20Stepper%20Motor%20Controller%20SMD1478250.pdf
> 
> and
> 
> http://www.motioncontrolproducts.co.uk/redirect.php?action=url&goto=www..motioncontrolproducts.co.uk%2Fpdf%2FMSD980datasheet.pdf
http://www.motioncontrolproducts.co.uk/pdf/MSD980datasheet.pdf

Actually neither are totally up to date with the units as currently shipped!
The USED to be +18 to +80V ( and even the MCP sheet still has that in the P2 
input section ;) ) but the units as shipped now are labelled 24V to 90V

70 to 80V is safe now while previously one would have kept below 70V.

-- 
Lester Caine - G8HFL
-----------------------------
Contact - http://lsces.co.uk/lsces/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk//
Firebird - http://www.firebirdsql.org/index.php

Guy Fawkes wrote:
> On 3 Aug, 12:30, NoSpam  wrote:
>> I'm gradually becoming seduced by the idea of CNC on a mill. The
>> question is whether to convert my Tom Senior M1 to CNC, or whether to
>> buy a KX1 or a KX3 - to be honest I like the idea of a new toy!
>>
>> Some questions:
>> - Has anyone here got any opinions on the KX1 or KX3 compared to an M1?
>>
>> - Has anyone in the South got a KX1 or KX3 running that I could have a
>> look at (within striking-range of Winchester)?
>>
>> - How easy/hard is it to convert an M1 to CNC? (I'll ask in the TS
>> owner's group too)
>>
>> - Never having used CNC before, if I bought a KX3 would I want to keep
>> the M1 for manual work or is it reasonable to plan to do everything with
>> CNC?
>>
>> Dave
> 
> First off, YMMV, however...
> 
> I decided to go down the "convert a decent old fashioned mill" route
> for several reasons, I know I'm starting with a quality machine, I
> know I can spec EVERY single component to my own desires, and perhaps
> most of all because I think that having done a conversion I will be
> more able to understand and therefore use the thing properly...

... snipped
> 
> Any questions ask away, or if you're in the southwest you can always
> drop by and nose around.
> 
> Cost wise I can convert both the mill and lathe to CNC for less than
> 400 quid all in, and that is all quality branded industrial products
> made to spec, no fleabay stuff, no chinese stuff, none of that.

How did you solve the problems of backlash and leadscrew wear? I've got 
new nuts(!) but there's always going to be some play/wear.
I've read that ball leadscrews aren't a good idea for CNC/manual mills 
because when used manually there isn't enough resistance - but I'm not 
convinced that wouldn't be insurmountable by either programming 
resistance via the steppers or adding a friction device - - any thoughts 
about this?

Dave

On 4 Aug, 14:43, NoSpam  wrote:

> How did you solve the problems of backlash and leadscrew wear? I've got
> new nuts(!) but there's always going to be some play/wear.

Backlash and leadscrew (wear) mapping is built into Mach3.

> I've read that ball leadscrews aren't a good idea for CNC/manual mills
> because when used manually there isn't enough resistance

well, you have to really lock down the axes when manual milling.

>- but I'm not
> convinced that wouldn't be insurmountable by either programming
> resistance via the steppers or adding a friction device - - any thoughts
> about this?

Yeah, ballscrews are bloody expensive by the time you've bought decent
ballnuts and bearings, and the fact is a ballscrew will not suddenly
make your machine more accurate, they reduce stiction and friction to
minimal amounts but that doesn't actually affect accuracy and
repeatability...

You can always retrofit ballscrews later, if you think it is worth
it...

Guy Fawkes wrote:
> On 4 Aug, 14:43, NoSpam  wrote:
> 
>> How did you solve the problems of backlash and leadscrew wear? I've got
>> new nuts(!) but there's always going to be some play/wear.
> 
> Backlash and leadscrew (wear) mapping is built into Mach3.
> 
... snipped

I've just scanned through the manual and found that backlash can be 
programmed so that it "knows" how far to back-up, but I think this 
disables corners and a couple of other functions - so maybe ballscrews 
will be needed.
I couldn't find anything about leadscrew mapping, where is this documented?

Whilst scanning I noticed that glass DROs can be connected - a nice feature!

Dave

On Mon, 4 Aug 2008 11:00:42 -0700 (PDT), Guy Fawkes
 wrote:

>Yeah, ballscrews are bloody expensive by the time you've bought decent
>ballnuts and bearings, and the fact is a ballscrew will not suddenly
>make your machine more accurate, they reduce stiction and friction to
>minimal amounts but that doesn't actually affect accuracy and
>repeatability...

...and unless you go for antibacklash ballnuts, they won't remove
backlash either.

The big "plus" with ballscrews over and above the increased efficiency
is that they wear much more slowly than conventional threads, so the
accuracy, repeatability, etc. changes very slowly over time compared
with conventional threads.

Regards,
Tony

On 5 Aug, 10:35, NoSpam  wrote:

> I've just scanned through the manual and found that backlash can be
> programmed so that it "knows" how far to back-up, but I think this
> disables corners and a couple of other functions - so maybe ballscrews
> will be needed.
> I couldn't find anything about leadscrew mapping, where is this documented?
>
> Whilst scanning I noticed that glass DROs can be connected - a nice feature!
>
> Dave

To be honest I'm still learning the software and configuring the
system, so I can't point you at official documentation for each
feature that I have found and played with...

Agreed about the DRO input, in my case it makes my playing an
iterative game of pinning the tail on the donkey.

HTH

On 5 Aug, 10:35, NoSpam  wrote:

>
> I've just scanned through the manual and found that backlash can be
> programmed so that it "knows" how far to back-up, but I think this
> disables corners and a couple of other functions - so maybe ballscrews
> will be needed.
> I couldn't find anything about leadscrew mapping, where is this documented?
>
> Whilst scanning I noticed that glass DROs can be connected - a nice feature!
>
> Dave

I see your in Winchester, about 90 odd minutes away by road, if you
want to come down and play (M5 J30) with actual stuff gissa shout.

On 5 Aug, 10:39, Tony Jeffree  wrote:
> On Mon, 4 Aug 2008 11:00:42 -0700 (PDT), Guy Fawkes
>
>  wrote:
> >Yeah, ballscrews are bloody expensive by the time you've bought decent
> >ballnuts and bearings, and the fact is a ballscrew will not suddenly
> >make your machine more accurate, they reduce stiction and friction to
> >minimal amounts but that doesn't actually affect accuracy and
> >repeatability...
>
> ...and unless you go for antibacklash ballnuts, they won't remove
> backlash either.
>
> The big "plus" with ballscrews over and above the increased efficiency
> is that they wear much more slowly than conventional threads, so the
> accuracy, repeatability, etc. changes very slowly over time compared
> with conventional threads.

Oh come on, ballscrews DO wear and suffer other forms of damage, and
my leadscrews are at present 30 years old and yet by "coming back" on
backlash I could approach a thou manually, with the DRO considerably
better.

Sure, ballscrews wear LESS than trapezoidal by definition because
there is less friction and stiction, but "less" is a relative term,
and PLEASE do not let us fall into the trap of thinking that just
because our CNC software allows us to "work" to an apparent accuracy
of a thousandth of a micron our actual physical machine tool and
tooling suddenly got orders of magnitude more accurate.

My X axis "glass" scale is about 750 mm long and has a coefficient of
linear expansion about a tenth of aluminium or a fifth of the cast
iron machine table, but even so, 15 degrees celcius ambient range
between seasons means worrying about a theoretical trapezoidal
leadscrew wearing at maybe a tenth of a thou (if you do not maintain
it) a year is pretty pointless.

My initial tests show that the discrepancy between what the
uncalibrated mach3 software things the positions are and what the DRO
reports they actually are for any meaningful sized work that will fit
in my mill is of the order of 1.1 thou on the Y and 2.2 thou on the X,
already that is better than the deflection I'll get running a 3 mill
endmill on a cut with a full chip load per tooth... if I can get a
practical repeatable accuracy out of this thing under CNC control of
approaching a thou I will be over the moon.

Practical repeatable accuracy means measuring the part machined
compared to the dimensions it is supposed to be, actually measuring
the finished part, not reading the numbers off the idiot box.

For 99% of scenarios a practical repeatable dimensional accuracy of 5
thou will make me happy and consider the investment of time and effort
in the CNC conversion to be throughly worthwhile.

Perhaps Mr Stephenson will have some comments about how rigid 16mm end
mills are when told to cut a perfectly perpendicular slot in something
nice and soft like alu, and how perpendicular the CMM says the
finished product is after a single pass.

Guy Fawkes wrote:
> On 4 Aug, 14:43, NoSpam  wrote:
> 
>> How did you solve the problems of backlash and leadscrew wear? I've got
>> new nuts(!) but there's always going to be some play/wear.
> 
> Backlash and leadscrew (wear) mapping is built into Mach3.
> 
>> I've read that ball leadscrews aren't a good idea for CNC/manual mills
>> because when used manually there isn't enough resistance
> 
> well, you have to really lock down the axes when manual milling.
> 
>> - but I'm not
>> convinced that wouldn't be insurmountable by either programming
>> resistance via the steppers or adding a friction device - - any thoughts
>> about this?
> 
> Yeah, ballscrews are bloody expensive by the time you've bought decent
> ballnuts and bearings, and the fact is a ballscrew will not suddenly
> make your machine more accurate, they reduce stiction and friction to
> minimal amounts but that doesn't actually affect accuracy and
> repeatability...
> 
> You can always retrofit ballscrews later, if you think it is worth
> it...


I asked a similar question on the Mach3 forum, here's the reply (for info):

"This reply is contentious but IMO there is no sensible way to
compensate for backlash on a machine your size because the cutting
forces will drag the table around. The control system will be
hopelessly non-linear as the motor has to turn quite a few degrees
befor the table moves at all then it suddenly starts moving at the
commanded speed. Little Taigs etc. have enough friction that some users
get away with Mach's backlash compensation. But it can never be better
that a bodge.
Fit ballscrews or, probably better, sell the Senior and buy a machine
that already has them to retrofit with Mach."

This implies that stiction may be a problem too, have you done much 
metal cutting yet to see how well it works in practice?

Dave

On Tue, 5 Aug 2008 06:26:54 -0700 (PDT), Guy Fawkes
 wrote:

>Oh come on....

<Assorted red herrings (or were they smoked kippers?) snipped>

Are you done with your rant yet?

Regards,
Tony

"Guy Fawkes"  wrote in message 
news:3b95177e-47e9-484a-8a63-a47540b30698@t54g2000hsg.googlegroups.com...
> On 5 Aug, 10:39, Tony Jeffree  wrote:
>> On Mon, 4 Aug 2008 11:00:42 -0700 (PDT), Guy Fawkes
>>
>>  wrote:
>> >Yeah, ballscrews are bloody expensive by the time you've bought decent
>> >ballnuts and bearings, and the fact is a ballscrew will not suddenly
>> >make your machine more accurate, they reduce stiction and friction to
>> >minimal amounts but that doesn't actually affect accuracy and
>> >repeatability...
>>
>> ...and unless you go for antibacklash ballnuts, they won't remove
>> backlash either.
>>
>> The big "plus" with ballscrews over and above the increased efficiency
>> is that they wear much more slowly than conventional threads, so the
>> accuracy, repeatability, etc. changes very slowly over time compared
>> with conventional threads.
>
> Oh come on, ballscrews DO wear and suffer other forms of damage, and
> my leadscrews are at present 30 years old and yet by "coming back" on
> backlash I could approach a thou manually, with the DRO considerably
> better.
>
> Sure, ballscrews wear LESS than trapezoidal by definition because
> there is less friction and stiction, but "less" is a relative term,
> and PLEASE do not let us fall into the trap of thinking that just
> because our CNC software allows us to "work" to an apparent accuracy
> of a thousandth of a micron our actual physical machine tool and
> tooling suddenly got orders of magnitude more accurate.
>
> My X axis "glass" scale is about 750 mm long and has a coefficient of
> linear expansion about a tenth of aluminium or a fifth of the cast
> iron machine table, but even so, 15 degrees celcius ambient range
> between seasons means worrying about a theoretical trapezoidal
> leadscrew wearing at maybe a tenth of a thou (if you do not maintain
> it) a year is pretty pointless.
>
> My initial tests show that the discrepancy between what the
> uncalibrated mach3 software things the positions are and what the DRO
> reports they actually are for any meaningful sized work that will fit
> in my mill is of the order of 1.1 thou on the Y and 2.2 thou on the X,
> already that is better than the deflection I'll get running a 3 mill
> endmill on a cut with a full chip load per tooth... if I can get a
> practical repeatable accuracy out of this thing under CNC control of
> approaching a thou I will be over the moon.
>
> Practical repeatable accuracy means measuring the part machined
> compared to the dimensions it is supposed to be, actually measuring
> the finished part, not reading the numbers off the idiot box.
>
> For 99% of scenarios a practical repeatable dimensional accuracy of 5
> thou will make me happy and consider the investment of time and effort
> in the CNC conversion to be throughly worthwhile.
>
> Perhaps Mr Stephenson will have some comments about how rigid 16mm end
> mills are when told to cut a perfectly perpendicular slot in something
> nice and soft like alu, and how perpendicular the CMM says the
> finished product is after a single pass.

I doubt JS would use a four flute end mill  to machine a perfect slot,  it's 
not what they are for.  I suspect that a two flute cutter aka a slot drill 
is probably what you meant.

Is it possible to comment on cutter deflection without knowing the feed 
rate,  cutter accel and depth of cut?

On 5 Aug, 20:48, NoSpam  wrote:
> Guy Fawkes wrote:
> > On 4 Aug, 14:43, NoSpam  wrote:
>
> >> How did you solve the problems of backlash and leadscrew wear? I've got
> >> new nuts(!) but there's always going to be some play/wear.
>
> > Backlash and leadscrew (wear) mapping is built into Mach3.
>
> >> I've read that ball leadscrews aren't a good idea for CNC/manual mills
> >> because when used manually there isn't enough resistance
>
> > well, you have to really lock down the axes when manual milling.
>
> >> - but I'm not
> >> convinced that wouldn't be insurmountable by either programming
> >> resistance via the steppers or adding a friction device - - any thoughts
> >> about this?
>
> > Yeah, ballscrews are bloody expensive by the time you've bought decent
> > ballnuts and bearings, and the fact is a ballscrew will not suddenly
> > make your machine more accurate, they reduce stiction and friction to
> > minimal amounts but that doesn't actually affect accuracy and
> > repeatability...
>
> > You can always retrofit ballscrews later, if you think it is worth
> > it...
>
> I asked a similar question on the Mach3 forum, here's the reply (for info):
>
> "This reply is contentious but IMO there is no sensible way to
> compensate for backlash on a machine your size because the cutting
> forces will drag the table around. The control system will be
> hopelessly non-linear as the motor has to turn quite a few degrees
> befor the table moves at all then it suddenly starts moving at the
> commanded speed. Little Taigs etc. have enough friction that some users
> get away with Mach's backlash compensation. But it can never be better
> that a bodge.
> Fit ballscrews or, probably better, sell the Senior and buy a machine
> that already has them to retrofit with Mach."
>
> This implies that stiction may be a problem too, have you done much
> metal cutting yet to see how well it works in practice?
>
> Dave

1/ grab a dial gauge and a spring scale and measure how much force it
takes to drag your table around the backlash.

2/ assume something fairly standard like a 6mm end mill and apply
those forces to it and see / measure what happens.

I could possibly move the table roughing or hogging, but if I'm
roughing or hogging I don't care about a couple of thou, if I'm
finishing and I care about cutter deflection amongst other things, I
can't put enough force into the work to move the table around, but
don't take my word for it, this is easy enough to measure.

what you're getting here is people who wanted ballscrews, who bought
ballscrews, and who don't want to hear anything else about anything
else.... you don't HAVE to go to the expense of a ballscrew to
eliminate backlash either, if it is that much of an issue, but like I
said, go and measure your table, numbers don't lie.

On 6 Aug, 09:14, "Steve"  wrote:
> "Guy Fawkes"  wrote in message
>
> news:3b95177e-47e9-484a-8a63-a47540b30698@t54g2000hsg.googlegroups.com...
>
>
>
> > On 5 Aug, 10:39, Tony Jeffree  wrote:
> >> On Mon, 4 Aug 2008 11:00:42 -0700 (PDT), Guy Fawkes
>
> >>  wrote:
> >> >Yeah, ballscrews are bloody expensive by the time you've bought decent
> >> >ballnuts and bearings, and the fact is a ballscrew will not suddenly
> >> >make your machine more accurate, they reduce stiction and friction to
> >> >minimal amounts but that doesn't actually affect accuracy and
> >> >repeatability...
>
> >> ...and unless you go for antibacklash ballnuts, they won't remove
> >> backlash either.
>
> >> The big "plus" with ballscrews over and above the increased efficiency
> >> is that they wear much more slowly than conventional threads, so the
> >> accuracy, repeatability, etc. changes very slowly over time compared
> >> with conventional threads.
>
> > Oh come on, ballscrews DO wear and suffer other forms of damage, and
> > my leadscrews are at present 30 years old and yet by "coming back" on
> > backlash I could approach a thou manually, with the DRO considerably
> > better.
>
> > Sure, ballscrews wear LESS than trapezoidal by definition because
> > there is less friction and stiction, but "less" is a relative term,
> > and PLEASE do not let us fall into the trap of thinking that just
> > because our CNC software allows us to "work" to an apparent accuracy
> > of a thousandth of a micron our actual physical machine tool and
> > tooling suddenly got orders of magnitude more accurate.
>
> > My X axis "glass" scale is about 750 mm long and has a coefficient of
> > linear expansion about a tenth of aluminium or a fifth of the cast
> > iron machine table, but even so, 15 degrees celcius ambient range
> > between seasons means worrying about a theoretical trapezoidal
> > leadscrew wearing at maybe a tenth of a thou (if you do not maintain
> > it) a year is pretty pointless.
>
> > My initial tests show that the discrepancy between what the
> > uncalibrated mach3 software things the positions are and what the DRO
> > reports they actually are for any meaningful sized work that will fit
> > in my mill is of the order of 1.1 thou on the Y and 2.2 thou on the X,
> > already that is better than the deflection I'll get running a 3 mill
> > endmill on a cut with a full chip load per tooth... if I can get a
> > practical repeatable accuracy out of this thing under CNC control of
> > approaching a thou I will be over the moon.
>
> > Practical repeatable accuracy means measuring the part machined
> > compared to the dimensions it is supposed to be, actually measuring
> > the finished part, not reading the numbers off the idiot box.
>
> > For 99% of scenarios a practical repeatable dimensional accuracy of 5
> > thou will make me happy and consider the investment of time and effort
> > in the CNC conversion to be throughly worthwhile.
>
> > Perhaps Mr Stephenson will have some comments about how rigid 16mm end
> > mills are when told to cut a perfectly perpendicular slot in something
> > nice and soft like alu, and how perpendicular the CMM says the
> > finished product is after a single pass.
>
> I doubt JS would use a four flute end mill  to machine a perfect slot,  it's
> not what they are for.  I suspect that a two flute cutter aka a slot drill
> is probably what you meant.

I don't think I said anything about the number of flutes, but 4 flute
instead of 2 is legitimate if like me your spindle rpm is limited to
2500

>
> Is it possible to comment on cutter deflection without knowing the feed
> rate,  cutter accel and depth of cut?

in the sense that cutter deflection != zero, and 2 thou backlash is
easily exceeded by cutter deflection, yeah, it is.

in the sense that it is also easy to measure the amount of force
needed to overcome friction and move the tables around backlash (eg
circular pocketing) then you can work back from that force to material
removal rate and work back from that to mill dimensions and mix mill
dimensions with the force to get mill deflection

what gets me here is this whole attitude that just because the cnc
software works in hundreths of a micron bolting it on to a machine
tool is suddenly going to make that machine tool inherently more
accurate, making something fairly simply like a carb manifold accurate
to a thou in every direction is both un-necessary and a bloody sight
harder (and slower) than people assume, but just because the software
says it is so people assume it is so, and don't want to hear
different.

If I had a quid for every time I've offered to take a made part to a
CMM and compare notes to what the gcode said it was making, for free,
hell I'll buy you beer and lunch if you like, and not one person has
ever taken me up on it, why not, what can they possibly be afraid of
from the output of a certified and calibrated CMM?... the ONLY thing
it can tell them is the actual dimensions of the object, ergo they
don't want to know, so why don't they want to know.

but then I'm just ranting aren't I, and those who have splashed out on
ballscrews have the technical high ground merely because they have
splashed out on ballscrews.

Like I said, if my CNC conversion ends up being good for a thou I will
be absolutely over the moon.

On Wed, 6 Aug 2008 02:35:17 -0700 (PDT), Guy Fawkes
 wrote:

<More ranting snipped>

>what you're getting here is people who wanted ballscrews, who bought
>ballscrews, and who don't want to hear anything else about anything
>else.... you don't HAVE to go to the expense of a ballscrew to
>eliminate backlash either

Nobody apart from you has suggested that you had to have ballscrews
for backlash elimination, as far as I can tell.

Regards,
Tony

On Wed, 6 Aug 2008 02:49:30 -0700 (PDT), Guy Fawkes
 wrote:

<More ranting and smoked fish snipped>

>but then I'm just ranting aren't I, 

Yes.

>and those who have splashed out on
>ballscrews have the technical high ground merely because they have
>splashed out on ballscrews.

Rubbish.

Regards,
Tony

On 6 Aug, 11:02, Tony Jeffree  wrote:
> On Wed, 6 Aug 2008 02:49:30 -0700 (PDT), Guy Fawkes
>
>  wrote:
>
> <More ranting and smoked fish snipped>
>
> >but then I'm just ranting aren't I,
>
> Yes.


well that's your opinion and you're entitled to it, which is why I
suggested the other guy actually measure the force required to move
the table around backlash.

let's wait and see if he is the first example I have ever seen
(excepting linear rails and ballscrews) where the cutter can make
finishing cuts and overcome friction and stiction and move the table
around the backlash slack

I get the distinct impression I have trod in
something................................

John S

John S wrote:
> I get the distinct impression I have trod in
> something................................


Easily done ;)   Some just want to make a meal of it!


Wayne.....

Guy Fawkes wrote:

> [...] why I
> suggested the other guy actually measure the force required to move
> the table around backlash.
> 
> let's wait and see if he is the first example I have ever seen
> (excepting linear rails and ballscrews) where the cutter can make
> finishing cuts and overcome friction and stiction and move the table
> around the backlash slack

Sorry to bring back controversy, but are linear rails much better than 
slides? How much better? Bronze or linear ball-bearings?


-- Peter Fairbrother

(who may be overimproving his tiny lathe to the extent that it bends...)

On 17 Aug, 18:47, Peter Fairbrother  wrote:
> Guy Fawkes wrote:
> > [...] why I
> > suggested the other guy actually measure the force required to move
> > the table around backlash.
>
> > let's wait and see if he is the first example I have ever seen
> > (excepting linear rails and ballscrews) where the cutter can make
> > finishing cuts and overcome friction and stiction and move the table
> > around the backlash slack
>
> Sorry to bring back controversy, but are linear rails much better than
> slides? How much better? Bronze or linear ball-bearings?
>
> -- Peter Fairbrother
>
> (who may be overimproving his tiny lathe to the extent that it bends...)

Linear rails are less friction and stiction than traditional slides
and gibs.

As to "better", you can whack a linear rail and forever bend it out of
true, you can't do that to a slide.