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Offline Davek0974

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Backlash...
« on: September 28, 2016, 01:32:51 PM »
I'm just at the final stages of testing on my high speed spindle attachment for my Bridgeport, running cut tests now.

Would backlash make holes smaller or bigger?

The holes are 3.1mm being cut with a 2mm single flute endmill and are coming up a little tight.

They are ok on the other machine so my guesses backlash?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Backlash...
« Reply #1 on: September 28, 2016, 02:45:59 PM »
Backlash would tend to make the hole out of round so it could well be like it is smaller.


Hood

Offline Davek0974

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Re: Backlash...
« Reply #2 on: September 28, 2016, 03:01:25 PM »
Hmm i guess so, does backlash comp actually work?

Any tried and trusted ways of assessing actual backlash - I know its there, just need to assess and maybe adjust or compensate.

I know it needs new bearings on the ball-screws, one axis is new but wrong type, other axis is old OEM type so still not ballscrew style but better than the new ones!

List price is over £100 per pair so i need to find the right ones here.
Have read that any angular-contact bearings that fit would be ok with the right shims - the originals are pre-ground so there are no shims needed.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Backlash...
« Reply #3 on: September 28, 2016, 03:16:48 PM »
Backlash is supposed to work in the CSMIO but I have never used/needed it so can't say from personal experience.

First thing to find out is if it is consistent along the length of travel, if it is then just plug the numbers into the backlash page and enable.

Easiest way to test is place a clock on the table and against the head, somewhere flat preferably and then with the smallest MPG or Jog  increment move onto the clock and keep going until it is zero then Zero the X DRO in Mach and then MPG/Jog the opposite way and watch the clock to see when it starts to move, the value in the DRO will be the backlash. Repeat for Y but this time you can have the clock on the knee and have the tip against the saddle.

Hood

Offline Davek0974

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Re: Backlash...
« Reply #4 on: September 28, 2016, 03:21:26 PM »
Thanks, i'm sure there will be some variation as the ways are not worn evenly as normal on Bridgy so there will be more load on the screws at each end.

I'll run the tests and get some numbers but I really do need to find some bearings.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Backlash...
« Reply #5 on: September 28, 2016, 03:40:05 PM »
Try Bearing King and see what kind of price he can come up with for a  matched pair of angular contacts in the required size. I got a good price for the Spindle Bearings in my Beaver Mill, half the price I could get anywhere else and they were actually a better tolerance class as well.
I bought original bearings for the manual Bridgeport years ago and never used them, weren't cheap either LOL but for the life of me I can not remember where I put them.

Hood

Offline Davek0974

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Re: Backlash...
« Reply #6 on: September 29, 2016, 04:12:55 AM »
Bearing king seems ok, still a lot of ££££ at £122 per pair  - ouch
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline RICH

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Re: Backlash...
« Reply #7 on: September 29, 2016, 07:02:09 AM »
Quote
Would backlash make holes smaller or bigger?

Don't know as it's more complex than just a yes or no. ;)

I used backlash compensation (BC) for a long time. It's a work around that if applied appropriately
can compensate for the mechanical inaccuracies of machine components. The best solution is to
get rid of the backlash (minimize backlash is a better term ). BC coupled with good machine code
can accomplish machining a hole such that a bearing fits just right.

BUT ..... BC settings can vary and other component inaccuracies come into play when accuracy is desired.

Can elaborate more on this if you so desire.


RICH

Offline Davek0974

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Re: Backlash...
« Reply #8 on: September 29, 2016, 07:36:11 AM »
Feel free to elaborate at your leisure :)

I knew there would be some backlash, in fact i was pleased how little it is really for an old girl.

The holes are 3.1mm and a 3mm screw 'almost' fits so its not like its a country mile off size or coming out square :)

Yes I could drill them but that means another tool change and TBH the end mill makes a neater job out of them.

I will measure my slop and save up for the new bearings.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: Backlash...
« Reply #9 on: September 29, 2016, 01:56:42 PM »
Ok, seems there is a reasonably stable backlash of 0.1mm in Y and 0.13mm in X

Not so bad i think but can we improve with the compensation?

Are those the figures that are entered into it?

Backlash speed set at default?
« Last Edit: September 29, 2016, 01:59:11 PM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives