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Author Topic: Backlash...  (Read 7271 times)

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Re: Backlash...
« Reply #30 on: November 01, 2016, 08:34:42 PM »
Actually a gas spring is quite linear, which is why you use one instead of an ordinary spring.  A 90 lb gas spring with say a 10" stroke requires 90lbs of force to move it off the stop.  At full compression the force is only about 10% higher or about 100 lbs!  On my Z axis I have two gas springs back to back for a longer stroke because otherwise it drifts right down when the drives shut off.  The Z stroke is 18"

Offline stirling

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Re: Backlash...
« Reply #31 on: November 02, 2016, 05:23:37 AM »
FWIW Dave - I can't for the life of me see how BC can co-exist with CV - particularly with lots of V small moves.

Offline Davek0974

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Re: Backlash...
« Reply #32 on: November 02, 2016, 05:51:14 AM »
Thats probably why it sounds so rough, I think i'll leave it off and do some accuracy tests, I may be chasing ghosts here.

V-Carve G-Code is evil, probably the nastiest code possible as it is thousands of minute moves in all axes all at once.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline dude1

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Re: Backlash...
« Reply #33 on: November 02, 2016, 06:05:17 AM »
Dave Vcarve is the best thing to test with if it's bad after a 1000 lines of code it will be ok on 2D only, if it's good you're all set. I test with a V carve file that has around 1000 moves on each axis I can get it to 0.002

Offline Davek0974

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Re: Backlash...
« Reply #34 on: November 02, 2016, 03:44:58 PM »
Did some V-Carve tests tonight, 28000 lines, 38mins run time, it will run with BC on but sounds happier with it off, physical results look the same.

Will do some proper mill cuts ASAP.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline stirling

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Re: Backlash...
« Reply #35 on: November 03, 2016, 05:46:38 AM »
I reckon you're trying to make a silk purse out of a sow's ear here Dave. Looking at your test text toolpath you posted elsewhere, some of those moves are an order of magnitude less than your backlash. Is it really sensible to use a 0.2mm engraving bit with thousands of moves of a few 100ths of a mm on a Bridgeport I wonder?

Offline Davek0974

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Re: Backlash...
« Reply #36 on: November 03, 2016, 06:23:03 AM »
:) I like pushing the envelope :)

It seems to work ok so I can't see any harm in it, if it was too bad I would expect broken tools but this one seems fine after running these tests and it wasn't new when i started.

I know it's not an engraving machine as such, but it does seem to function pretty well as one, I don't do much engraving luckily but needed to know if it was possible and it seems so.

I still have the mini-mill but really need to sell that on now to recover space in the shop as well as cash.

I think she will do just fine but being me I like to know exactly what limitations i have :)

Just for completeness, the "test" is pictured below, the T is about 18mm tall, this picture was taken before i fitted the new thrust bearings on X & Y, its even better now.
« Last Edit: November 03, 2016, 06:33:32 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline RICH

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Re: Backlash...
« Reply #37 on: November 03, 2016, 07:04:13 AM »
FWIW,
Backlash becomes a killer when the size of the engraving / machining is real small.
A good "size test" would be to do a simple  letter  like "E".  
Tool tip radius comes into play, so for the "E" a depth of say .002" with width of machined line .003" the smallest overall size would be
.015" ( using high speed spindle and slow feed).

Tool breakage with small end mills becomes a problem and BC doesn't fix it.

I built  a machine just for engraving.
http://www.machsupport.com/forum/index.php/topic,6904.msg45266.html#msg45266

Most will not go to that extreme in size.
http://www.machsupport.com/forum/index.php/topic,13398.msg87957.html#msg87957

RICH
« Last Edit: November 03, 2016, 07:11:26 AM by RICH »

Offline stirling

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Re: Backlash...
« Reply #38 on: November 03, 2016, 07:09:09 AM »
Must have got the wrong end of the stick - sorry. I thought the point of the thread was that you had issues. If you're happy - I'll get back in my box.

Offline RICH

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Re: Backlash...
« Reply #39 on: November 03, 2016, 07:14:57 AM »
Stirling,
You can't leave, one need only  hit the top of the box and you will come popping up.  :D  ???  ;)

RICH