BOSS 1 stepper to servo retro?

[highly]

I've spent much of the last week searching around and have read the first 100 pages of threads dealing with BOSS conversions. I didn't find a clear answer, so here goes.

I recently picked up a Bridgeport Series 1 BOSS 5 rigid head machine (#CNC4242) for retro. I'd love to convert it to servos but the 1:1 factory ratio with 5tpi ballscrews concerns me a little bit. The math says 2:1 to 2.5:1 would be a much better choice, but I don't see room on the Y axis to fit as big a timing gear as I'd need without cutting things up, changing to a different belt pitch, or using multiple reductions. Ajax and others offer a kit but mention nothing about mechanical changes for a servo upgrade.

What is the recommendation for such a conversion? The intended servos are the KL34-180-90's (3200 RPM@90v). This is not my first CNC, but would be my first servo setup.

I know this is my first post here, but I tend to find the answers to my questions without posting. Sorry if this has been covered before, but if it has I couldn't find it!

Thanks!
Todd
==> Photos <==

[highly]

Mmmm. Crickets.
I'm looking into ways to replace the H100 pitch belt drive with something with more versatile timing gear sizes. Maybe GT2 5mm pitch. I'll be pulling the Y axis and seeing exactly how much space I have to work with.
I'd still really appreciate any advice or thoughts on the subject, though!

[cncsnw]

With Centroid and Ajax controls, I use 29 in-lb servo motors and run 1:1 (5 motor turns per inch of travel). If you can change it to 2:1 (10 motor turns per inch of travel) then you could go down to ca. 15 in-lb motors.

What is the continuous torque rating of your motors?

The 5mm pitch GT2 pulleys should work well.

[highly]

Thanks for the reply!

I managed to tear down the axis this weekend. The ballscrew came out easier than expected. The BearHug nut that holds the timing pulley to the ballnut, on the other hand, lived up to its name! I finally got it removed and was able to take measurements and verify that I could get a 60-tooth GT2 5mm pitch X 15mm belt width pulley on the screw. I ordered up the 60 tooth for the X and Y screws, belts, and some 20 and 24 tooth pinions for the servos. This will give me options for both 2.5:1 and 3:1 ratios on both axes. I plan to design in enough allowance into the motor adapters to fit from a 20 to a 30 pinion with the same belt (making 2:1, 2.5:1, and 3:1 possible. I hate being backed into a corner by poor choices early on!).

I'm just glad I should be able to fit the ratios I need in the space available.

The servo I am looking at is the Keling KL34-180-90. It is rated at about 14 in-lb continuous @ 90v, so 2.5:1 should get me plenty of torque. They are rated 3200 RPM @ 90v, so depending on the power supply voltage that should get me all the rapid I'd want. Drives will be Geckos unless I can source a 90v supply in which case I will go with Vipers.

As things start coming together I will create a build thread.

Thanks
Todd
"HighlyCaffeinated"

[Timvmax]

Hi Todd,
how are you getting on with the conversion?
I'm looking to go down the servo route with a series 2 so any advice would be greatly appreciated
Tim.

[colin1544]

Hello todd
I did an Ajax conversion about 6 years ago and have been very pleased with it I used the origonal belt and pulley set up and it worked fine very accurate, but recently I have been loosing accuracy on the X & Y axis by about 0.001 and have put it down to the drive belts which over the years have got oil soaked on the X axis and a bit brittle on the Y axis. These origonal belts seem to be hard to get hold of, so if anyone has any spares I would be most greatful. The spindle I have put in place a Teco inverter which is fine on low gear but it lacks torque below 600RPM in high gear range and I am eventualy going to look at replacing the origonal pulleys and belt with a Polyvee belt with a lower ratio to regain the torque at low revs. All in all the conversion has been good and the difference in programming is great, alot quicker easier and more flexible. Hope this helps Cheers Colin.