Converting an AMAT25LV

[Davek0974]

I run toothed belt on both my mills, the bigger one has a heavy table and servo drives, if the belt is tightened just right there is no backlash to compensate for at all. The belt can move slightly but when that movement is converted to rotation and then reduced by the screw pitch, the actual distance linear is microscopic.

I have tried backlash comp and i would not recommend it to anyone - always get the system mechanically sound and unless you are working to nuclear industry standards, just learn to live with the tiny backlash we have - there will ALWAYS be backlash or the system would not move, its just a matter of knowing how much.

[Lloyd Barnes]

I run toothed belt on both my mills, the bigger one has a heavy table and servo drives, if the belt is tightened just right there is no backlash to compensate for at all. The belt can move slightly but when that movement is converted to rotation and then reduced by the screw pitch, the actual distance linear is microscopic.

I have tried backlash comp and i would not recommend it to anyone - always get the system mechanically sound and unless you are working to nuclear industry standards, just learn to live with the tiny backlash we have - there will ALWAYS be backlash or the system would not move, its just a matter of knowing how much.

yep, couldn't agree more, do it right, do it once etc. I just wasn't sure whether switching from a direct drive to a belt drive inevitably introduced a hint more backlash regardless of how perfectly you tune the belt tension. Always faster/cheaper to learn from others mistakes etc. Should have the belt drive put together over the next few days so will be able to test backlash on all the axis.

As you say we're not working to nuclear standards. I'm generally machining car parts on the mills, and the tolerances don't need to be that high. Its just I'm tired of using the Bridgeport like an oversized etch a sketch to try to make curved parts!

[Davek0974]

yep, couldn't agree more, do it right, do it once etc. I just wasn't sure whether switching from a direct drive to a belt drive inevitably introduced a hint more backlash regardless of how perfectly you tune the belt tension. Always faster/cheaper to learn from others mistakes etc. Should have the belt drive put together over the next few days so will be able to test backlash on all the axis.

As you say we're not working to nuclear standards. I'm generally machining car parts on the mills, and the tolerances don't need to be that high. Its just I'm tired of using the Bridgeport like an oversized etch a sketch to try to make curved parts!

I thought you were converting an AMAT25LV ?

My Bridgeport CNC conversion was the best thing i ever did, it makes it a much more useful machine. The backlash i do have comes mainly from the screw thrust bearings - in the end i bought new units here and it helped massively, not cheap though. The next is screw nut slop - I just fitted a standard Bridgeport conversion screw set from the USA, its good but not excellent. I have less than 0.1mm backlash in both axes and i don't think thats too bad for an old girl :)

[Lloyd Barnes]

I thought you were converting an AMAT25LV ?

My Bridgeport CNC conversion was the best thing i ever did, it makes it a much more useful machine. The backlash i do have comes mainly from the screw thrust bearings - in the end i bought new units here and it helped massively, not cheap though. The next is screw nut slop - I just fitted a standard Bridgeport conversion screw set from the USA, its good but not excellent. I have less than 0.1mm backlash in both axes and i don't think thats too bad for an old girl :)

Sorry not being clear am I. I have a series 1 Bridgeport but have bought the AMAT to convert to CNC. Sadly my Bridgeport, even though its a 1981 model is a bit worn. I can't adjust the gibs to acceptable play for a CNC machine without the ways tightening at the outer ends. Also I really wanted something I could enclose, the Bridgeport fills the shop with chips, and I'd didn't want to add to it by getting the coolant working too. I'll certainly keep it for general use where the part is not complex or for sizing stock for the AMAT etc.
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I read a load online and the general impression I got was converting a series 1 wasn't the best way to go, sounds like you disagree although perhaps you have a later model? I could certainly live with 0.1mm with the parts I make, not bad at all for a Series 1. I guess the bits were pretty pricey though?

[Davek0974]

Ok, got it, makes sense now.

I think you did the right thing, my BP can fling the chips a good 8' away but its only me so who cares :)

I was strongly advised NOT to convert the BP and that advice was right. The advise was to sell it and get an old CNC VMC etc and retrofit the electrics - this would have been ideal BUT i could not physically fit anything but a BP in my shop - not even a proper CNC BP. I also do not have the power capacity for the big spindle motors on CNC stuff.

Now i have used it a few times, I REALLY want a proper CNC mill with an auto tool changer. ;)

Total cost was silly money but once you dive in you cant back out.

[Lloyd Barnes]

Well, its about ready to go. I've taken the advice and setup the Z Axis with a 2:1 belt drive (very annoyingly I ordered the wrong belt length so just waiting now for the right one to come). Most of the rest of it is complete so once the belt is here its time to take a few trial cuts and see where it is. Y Axis NEMA23 with spindly legs is now mercifully covered up, cover plate for the X Axis next. Hopefully starting to cut some trial parts this weekend.
/p
Appreciate all the advice so far

[Davek0974]

Looking good :)