New Quill Drive Design

[M250cnc]

Hi Mike AKA TOTALLYRC

Valid point the issue will be flex but the outcome will be backlash.

As i said i speak from experience

Phil

[SCzEngrgGroup]

Ray i think you are going to get a lot of backlash with that design.

The ball screw is too far away from the quill.

The further away it is, the more backlash you will get.

I know this from experience on my RF31

I ended up with the ball screw very close to the quill and it is perfect but was a lot of modification to head casting so no kits available

Phil

Phil,

The ballscrew is actually about as close as it it physically possible to get it to the quill on a BP without removing large parts of the head casting. And, it's closer than those on the commercial BP quill drives I've seen, including the Anilam and Elrod. The "yoke" that attaches the ballnut to the quill is made of steel, and the way it's designed, I don't think it will flex noticeably at all. Certainly there is not enough force involved to bend the 1.25" thick "yoke", and the attachment to the quill is considerably stiffer than that on another commercial drive I have, which exhibits virtually no flex. And the yoke on that one is made of aluminum.

Well find out soon enough.....

Regards,
Ray L.

[Sparky_NY]

I am betting it will be just fine. I built one for a mill I have, very similar in design BUT with a cheapo Rotron ballscrew and a flat thrust ball bearing. Miine only ran .003 backlash and I am near positive all of it came from the screw and cheap bearings, none from flex of the arm going to the quill.

Also, worthy of note is that I drove the ballscrew with a 3:1 belt drive and a nema23 stepper, 425oz. I got 80 IPM and enough force to break drill bits with ease. With the size of the servo Himmy is using his should be able to do double duty as a 20 ton press!

[SCzEngrgGroup]

I am betting it will be just fine. I built one for a mill I have, very similar in design BUT with a cheapo Rotron ballscrew and a flat thrust ball bearing. Miine only ran .003 backlash and I am near positive all of it came from the screw and cheap bearings, none from flex of the arm going to the quill.

Also, worthy of note is that I drove the ballscrew with a 3:1 belt drive and a nema23 stepper, 425oz. I got 80 IPM and enough force to break drill bits with ease. With the size of the servo Himmy is using his should be able to do double duty as a 20 ton press!

Sparky,

Yes, I think I'll have more than enough thrust, and speed. The servo is the same one I use on X/Y, with the same total reduction (10:1). X and Y will do 400IPM, and will snap off 1/2" endmills without even losing position!

I'm not at all concerened about flex of the yoke. At 1.25", the chunk of steel is far too thick to flex, and the attachment is also very solid - it is not solely dependant on the bolt to keep it in place. Where it meets the quill it is over an inch tall, as wide as the opening in the head casting, and making full contact with the quill over that entire area. The bolt is located closer to the top than the bottom, since the highest forces will be seen when plunging. It *can't* move relative to the quill unless the steel compresses below the bolt on plunges, or above the bolt in retracts.

The screw is a good quality 20mm 5-pitch, with zero-backlash nut. The bearings are paired angular contact, also zero backlash.

Regards,
Ray L.

[SCzEngrgGroup]

Well, this is pretty darned cool! I took the servo motor off my knee, and mounted it on the quill drive, and did some quick testing. Without adjusting the servo tuning at all (which means it's WAY off!), I can get 200 IPM without breaking a sweat. The drive is smooth and quiet. Backlash is all by non-existant - WELL below 0.0005". I'll have a short video up in a little bit.

Regards,
Ray L.

[SCzEngrgGroup]

I've never posted a video here before. Hopefully this works:

"http://www.youtube.com/watch?v=M_AKhV9-eIk"]YouTube- P1050520.MOV

Regards,
Ray L.

[TOTALLYRC]

Hi Ray,
Looks to me to be a well executed design with plenty of beef where needed to prevent flexing.
To test for flex you could one step at a time run it into the table with a few indicators and see how much flex there is. I would bet that under normal machining forces the flex is minimal.


Mike

[SCzEngrgGroup]

Hi Ray,
Looks to me to be a well executed design with plenty of beef where needed to prevent flexing.
To test for flex you could one step at a time run it into the table with a few indicators and see how much flex there is. I would bet that under normal machining forces the flex is minimal.


Mike

Mike,

I'll do some better testing once it's complete. Right now, I don't even have keys in the pulleys, and I was running most of the day with an XL pulley on the motor, and a GT2 belt. It's much happier now that I have the right motor pulley. I'm also getting about 0.0005" flex in the mounting plate, since the top of the head is not on yet - had to order longer bolts to re-attach it.

Regards,
Ray L.

[redford1955]

have you considered being able to disconnect the quill drive to use the mill in 2 axis mode like a Bridgeport EZ trak?

keith

[SCzEngrgGroup]

have you considered being able to disconnect the quill drive to use the mill in 2 axis mode like a Bridgeport EZ trak?

keith

Keith,

I thought about it, but not very hard. I didn't see an obvious way to easily disconnect it while maintaining the very solid connection necessary for good CNC performance. And I don't use the other axes in manual mode, so don't really see the need to do so for the quill either. It's just as easy, if not more so, to just operate "manually" using my pendant.

Regards,
Ray L.

[SCzEngrgGroup]

The quill drive is done, except for the belt/pulley cover the ballscrew cover, a proper stop block to limit downward travel (to take the place of the bolt and stack of washers in there now), and the limit switches. The limits will be Hall Effect switches, that will sense the steel yoke.

Total travel is 5-5/32", which is the total travel of the quill with no drive installed. With limits set just inside this, I should still have probably 4-7/8" of usable quill travel.

Tomorrow I'll be taking the first test cuts with it, and I expect it to work very well. I'll be testing some wicked new endmills that are, in theory, capable of slotting 1/2" wide, >0.5" deep, at over 100 IPM! I won't be able to get it going quite that fast, but I am hoping to perhaps do 1/4" deep at 50-60 IPM. If I do it, I'll post a video. Should be fun to watch!

Regards,
Ray L.

[nate]

more videos please...

[SCzEngrgGroup]

more videos please...

Nate,

I will do that, next time I go out to the shop. Boy peck drilling is a WHOLE different experience at 200 IPM on the quill, as opposed to 50 IPM on the knee!

The quill drive is working great, but I've been unable to get much real work done, due to a flaky SmoothStepper. Unfortunately, the replacement is taking a long time to get here....

Regards,
Ray L.

[wdp67]

Ray
I just did a simular conversion on my quill, and I have a few questions. It seems that the quill has quite a bit of backlash on my mill, is there a way to deal with that? I am pretty sure my conversion is pretty solid, because I can not make the indicator move by tugging and pulling on the conversion parts. I can however grab where the quill handle goes and make the needle move. Your advice is greatly appreciated!!

Walt

[SCzEngrgGroup]

Ray
I just did a simular conversion on my quill, and I have a few questions. It seems that the quill has quite a bit of backlash on my mill, is there a way to deal with that? I am pretty sure my conversion is pretty solid, because I can not make the indicator move by tugging and pulling on the conversion parts. I can however grab where the quill handle goes and make the needle move. Your advice is greatly appreciated!!

Walt

Walt,

How does your drive attach to the quill? Thats the source of the little bit of flex I have in mine, and it appears to be due to the quill itself distorting. Certainly the yoke is not flexing, and there is no backlash in any of the mechanical bits.

Regards,
Ray L.

[wdp67]

Ray
I made a pretty heavy duty yoke that attaches to the quill using the original drilled and tapped hole in the quill, the yoke is cut out to fit around the ball screw and the nut screws to the yoke. I could not find a 3/8 x 24 allen head cap screw in town here so I used a bolt instead, and had to rig up a spacer because of the bolts length. I wonder if my spacer is causing all my trouble, I used a nylon spacer. Maybe I should turn a steel spacer?

Thanks
Walt

[SCzEngrgGroup]

Ray
I made a pretty heavy duty yoke that attaches to the quill using the original drilled and tapped hole in the quill, the yoke is cut out to fit around the ball screw and the nut screws to the yoke. I could not find a 3/8 x 24 allen head cap screw in town here so I used a bolt instead, and had to rig up a spacer because of the bolts length. I wonder if my spacer is causing all my trouble, I used a nylon spacer. Maybe I should turn a steel spacer?

Thanks
Walt

There is no way a nylon spacer will work. You need a *steel* spacer, and it should conform to the curvature of the quill, include a boss that fits snugly into the double-D recess in the quill, and must extend as far above and below the bolt as possible.

Regards,
Ray L.

[wdp67]

I think I did not explain myself clearly, My yoke does fit up tightly against the quill as you stated. My spacer is on the bolt between the bolt head and the yoke. I had to use a regular bolt instead of my original idea of a cap screw. I had drilled a countersink for the head of the allen head cap screw. I did not make the countersink big enough diameter to get a socket in it to tighten the bolt so I put a nylon spacer in there to be able to get on the head with a socket. Is that more clear or am I making it worse? Reguardless, I think I need to either find a cap screw or make a spacer out of steel.

Walt

[SCzEngrgGroup]

I think I did not explain myself clearly, My yoke does fit up tightly against the quill as you stated. My spacer is on the bolt between the bolt head and the yoke. I had to use a regular bolt instead of my original idea of a cap screw. I had drilled a countersink for the head of the allen head cap screw. I did not make the countersink big enough diameter to get a socket in it to tighten the bolt so I put a nylon spacer in there to be able to get on the head with a socket. Is that more clear or am I making it worse? Reguardless, I think I need to either find a cap screw or make a spacer out of steel.

Walt

A nylon spacer anywhere on the bolt will be roughly the equivalent of leaving the bolt loose. Under load, it will compress, allowing the yoke to move.

Regards,
Ray L.

[wdp67]

Thanks Ray,
Didn't mean to hijack your thread.

Walt