CNC RT

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1hand

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Hello,

I'm in the process of converting my RT's to cnc. One question now as I'm need to order the timing pulleys, is a 1:1 enough, or should it be a 2:1? I will be using 381 oz-in stepper on a 4" and 6" RT with 72:1.

Matt
 

1hand

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At 1:1 it would be producing 27,432 oz-in right? I should be able to do a direct mount and bypass the timing belt and pulley's with this kind of torque I would think. ???

Matt
 

cfellows

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Matt, your math sounds right, minus any losses for friction which can be considerable with a worm gear.

Chuck
 

stevehuckss396

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Sounds like you answered your own question.

BTW, I have never seen a RT that was belt driven.
 

1hand

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stevehuckss396 said:
Sounds like you answered your own question.

BTW, I have never seen a RT that was belt driven.
I had some old plans I found on the net, that was belt driven, but would take up valueable room, and extra expense also vs. a direct mount.

Matt
 

dieselpilot

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Unless you are using an encoder with low resolution or need more resolution than your stepper driver has to offer, there is no need to further reduce the motor output speed. I just mounted a rotary table with 90:1 gearing and a direct drive motor. I need to make a chuck adapter for 5C and chucks before I can use it. I've seen a few belt reduced rotary tables out there in use on home built CNC, but the driven pulley was mounted right on the 4th axis spindle, it didn't have a worm gear.

 

1hand

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I'm going to build some sorta equivalent of this mount.





Wish me luck!

Matt
 

kvom

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I have read that the main problem with "normal" rotabs under CNC as an A axis is that there is no automatic lock. Therefore the table can rotate under the force of the tooling by the amount of backlash in the system.

Unless you are turning the table while cutting you don't need a lot of torque. Most of the mill while turning applications seem to be engraving on a cylinder.

 

1hand

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kvom said:
I have read that the main problem with "normal" rotabs under CNC as an A axis is that there is no automatic lock. Therefore the table can rotate under the force of the tooling by the amount of backlash in the system.

Unless you are turning the table while cutting you don't need a lot of torque. Most of the mill while turning applications seem to be engraving on a cylinder.
So there is no power there unless its turning? That sucks! This totally blows my plans. Why would that be? Why would Mach 3 put gear cutting wizards on there software if your doing it manually anyway! Useless!

I can believe I've haven't come across this yet, poking around on the net.

Matt
 

Tin Falcon

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a stepper motor is at max torque when Idle so the motor will hold it but depending on the direction of force it max not hold completely due to back lash. you may just have to adjust out the back lash or make a new worm gear that meshes a bit tighter than the original. You do have a machine shop in your basement adapt and overcome.!!! yay just have to be smarter than the metal LOL
Tin
 

kvom

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what he said ^

If you are engraving, then the A axis will reverse a lot and the text or design can be distorted by the amount of backlash. That said, small DOC will make that much less of a problem, if any.
 

1hand

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Oh....I understand the backlash issue. I thought when you said no lock you meant, the stepper was dead at idle. That you could turn it with your fingers.

I can deal with backlash, but didn't know how to overcome keeping the stepper from not turning when its suppose to be stopped.

You Know what I mean?

Matt
 

RonGinger

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I just finished a rotary table using what looks exactly like the table you are using- I got it from Little Machine Shop. I mounted teh stepper as you are doing, except I used a piece of round stock instead of square.

I have cut a couple gears with it- 48dp, 20T and 40T for a Little Angel engine. Worked great. Backlash is not a problem since the gear program keeps moving the table in the same direction.

I used the Mach3 NFS wizards to generate the code (since I do the support for those wizards why would I use anything else :)

I am now working on a cam shaft cutting wizard. Ive got the math done, using the harmonic cam code from an old SIC magazine. If I get it working in time I will be running it on the demo KX1 at the Cabin fever show next weekend.
 

1hand

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RonGinger said:
I just finished a rotary table using what looks exactly like the table you are using- I got it from Little Machine Shop. I mounted teh stepper as you are doing, except I used a piece of round stock instead of square.

I have cut a couple gears with it- 48dp, 20T and 40T for a Little Angel engine. Worked great. Backlash is not a problem since the gear program keeps moving the table in the same direction.

I used the Mach3 NFS wizards to generate the code (since I do the support for those wizards why would I use anything else :)

I am now working on a cam shaft cutting wizard. Ive got the math done, using the harmonic cam code from an old SIC magazine. If I get it working in time I will be running it on the demo KX1 at the Cabin fever show next weekend.
Wow....that will be awesome.
Matt
 

shred

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1hand said:
Oh....I understand the backlash issue. I thought when you said no lock you meant, the stepper was dead at idle. That you could turn it with your fingers.

I can deal with backlash, but didn't know how to overcome keeping the stepper from not turning when its suppose to be stopped.

You Know what I mean?

Matt
RT's are typically driven by a worm gear. One of the things about worm gears is the worm can't be driven by the gear, so the only backlash you have to deal with is the lash between the worm and the wheel (which will not be zero or it wouldn't turn)

I use my CNC RT as a 4th-axis for workholding mostly-- it's easy to chuck up some round stock in the 3-jaw, mill a bit on one side, rotate 90 or 180 (or 60 or..) degrees and mill the other side(s). Not much CAD programming beyond a set of 2.5D layers. Here's making some fancy acorn nuts.. one program repeated six times-- when done, un-chuck, part off, drill and tap.








 

1hand

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shred,

are you locking down the rt after each move? or is the stepper holding it in each postion for the milling?
 

1hand

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who needs to buy hex rod anymore! :big:
 

1hand

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Got a little bit of a start on the mount today.

I had to remove the RT I was using to mill the TB5 flywheels, so I thought it would be a good time to tram the mill, before I put the milling vise back on.

...And it was off about .0015

I'm starting with a 2.25" square piece of 6061 for the mount.

First I squared 1 end.


Then flipped a found the edges and set the tool height.



Then it was time for the kiddo's to go to bed, No more noise for tonight.

til, tomorrow
Matt
 

shred

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1hand said:
shred,

are you locking down the rt after each move? or is the stepper holding it in each postion for the milling?
No locking. It's a standard worm-drive RT, so the stepper doesn't have to do much to hold it, but it is powered
They suggest locking for heavy cuts (the play in the worm/wheel can become a factor), but so far I've not needed to.

I'll have to get some pictures next time I'm making more complicated parts on the 4th.
 
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