Is there a simple way to motorize the cranks?

[TomB]

Has anyone added drive motors to a TriPower without getting into all the details of CNC. I like my TriPower, think it works really well but feel I’m really abusing it. It’s a 3 year old machine and I use it for both milling and turning. But it’s the Acme screw version with a DRO and everybody says it’s not suitable for CNC because of the backlash. However, I get tired of cranking and frequently use the threading drive/gears to just move the tool across the work. By doing so I’ve stripped gears (ever since I had to put the anti-backlash nuts back into the holder my machine cranks hard). I’ve thought that a motor attached to the drives would be a better approach. But I just want to set the cut up then flip a switch to move the tool and when it reaches the end of the cut flip the switch back off.

Simplistically all I should need is a 3-way switch for each axis with perhaps a pot to set the speed. I realize that can be done with a computer, but all the computer SW I’ve heard about is built around g-code, CAD and CAM and that seems way more complicated than I need or want. I’m computer literate but I don’t have the time to write an application for this and I don’t want SW that can do anything because complex SW has complex interfaces and I don’t have the time to learn that either.

Are there any simple solutions?

[smallblock]

Originally Posted by TomB Has anyone added drive motors to a TriPower without getting into all the details of CNC. I like my TriPower, think it works really well but feel I’m really abusing it. It’s a 3 year old machine and I use it for both milling and turning. But it’s the Acme screw version with a DRO and everybody says it’s not suitable for CNC because of the backlash. However, I get tired of cranking and frequently use the threading drive/gears to just move the tool across the work. By doing so I’ve stripped gears (ever since I had to put the anti-backlash nuts back into the holder my machine cranks hard). I’ve thought that a motor attached to the drives would be a better approach. But I just want to set the cut up then flip a switch to move the tool and when it reaches the end of the cut flip the switch back off. Simplistically all I should need is a 3-way switch for each axis with perhaps a pot to set the speed. I realize that can be done with a computer, but all the computer SW I’ve heard about is built around g-code, CAD and CAM and that seems way more complicated than I need or want. I’m computer literate but I don’t have the time to write an application for this and I don’t want SW that can do anything because complex SW has complex interfaces and I don’t have the time to learn that either. Are there any simple solutions?

In a word- no
I went down that path years ago with my 17-20 xmtc machine. There are several ways you can go;
1. DC motors with a controller and pot control for speed. The problem is finding one that has the right rpm and power for driving the table. Most of them run at pretty high speeds- about 6000 rpm- requiring a lot of gearing down to get a reasonable feed rate on the table.
2. DC gear reduction motors- these will get you the power and speed you need, but because of the gear reducer, it makes turning the handles by hand very difficult.

You can look at www.surpluscenter.com for low cost versions of the above.

3. A stepper driver ( chopper driver) and a stepper motor offer the type of RPM and torque you need and will bolt right up to your existing mounts. You can Google search them and find a lot of fairly inexpensive units out there. If you want to run more than 1 axis, then you will need to buy 3 motors and plug in the one you want to use.
HOWEVER- most of these drivers are very sensitive to what is known as an inductive spike. If you unplug the motor while the power is on, it will blow the circuit. So going that route, plan on some day forgetting to turn off the power and popping the board. It would seem that you could wire in a 3 position switch to select among the 3 motors, so no unplugging is necessary, but it requires a special switch called a ]make before break] to insure that the circuit is always completed during the switch over.
For a Tripower or Patriot size machine, you will need a driver with a minimum of 3 amps output and NEMA 34 frame size motors in the 350-400 OZ / IN torque range.

BTW- if your hand cranking is too hard, you probably adjusted the anti backlash nuts too close- anything less than 0.004" lash will start to be very hard to turn.

Good luck

[diecutter]

Are you thinking of something along these lines?

http://www1.mscdirect.com/CGI/NNSRIT...gename=listpag

[smallblock]

Originally Posted by diecutter Are you thinking of something along these lines? http://www1.mscdirect.com/CGI/NNSRIT...gename=listpag

Those are designed for the Bridgeport and various Chinese clones. Even if you could adapt them to a Tripower, after the cost for 3 units and the necessary modifications you could buy the 4 axis CNC system from Shopmaster.

[Arquibaldo]

This discussion might give you a few ideas:

http://www.machinistblog.com/make-or...our-mini-mill/

In particular, this seems to be an interesting homemade contraption:

http://www.progressivelogic.com/mf/powerfeed1.html

( I hope it isn't against forum rules to post these links; if it is, please have a moderator
remove them)

Nelson

[smallblock]

Originally Posted by Arquibaldo This discussion might give you a few ideas: In particular, this seems to be an interesting homemade contraption: http://www.progressivelogic.com/mf/powerfeed1.html Nelson

When I got my 17-20 xmtc, I was doing a lot of flywheel work. Turning across the face of a 14" disc was a real hand killer and hard to keep a consistent finish, so I also thought of the power drill idea. Back then I had a Ryobi drill and I decided just to hook it up to the Y axis handle and see what would happen. The shoptask handle was held by a special nut with a jam screw- much like the valve adjusters on roller rockers. The nut was too big in diameter for the drill chuck, so I just used a longer jam screw that protruded about an inch. I could grip this screw with the drill chuck and stand there and run the carriage back and forth with the drill. It had good speed control and plenty of power. The only problem was that the Ryobi and its battery pack were pretty heavy, so you couldn't let go of it or the weight would bend the jam screw. I used a couple of bungie cords hanging from the ceiling to support the drill if I needed to let go for a minute. The whole thing was really red neck looking, but I did a lot of turning with it. Later on I got a Patriot machine which had the gear driven power feeds on X,Y and Z, which was nice, but the drill still had the advantage of changing speeds on the fly.

[TomB]

I was pretty sure that there was no easy solution, althought I'm not really sure why not. I was sort of hoping that somebody made a pulse generator that could drive NEMA 34 steppers and be switched to any one of three drives. With proper switching I would think that unpowered steppers would not interfer with cranking. (I was aware of the BP table drive gear motors. I'm not sure they would work for the TriPower drives but I've been planning to buy one to mount to the bridge elevation crank for some time. If I had a motor on that crank I'd never want to do it manually.)

So given the comments I'll go buy three NEMA 34 motors plus some of Marris' Gecko controllers. The motors are pretty cheap and the TriPower came with belts and pulleys, the controller is a few hundred dollars and I probalby have an old but suitable PCs so the total is not too costly. Unfortunatily that will mean I have to set up a PC application to make a parallel port drive the stuff. Although the buying and building are not that disconcerting, I really did not want to get into the needed SW. I retired after writing SW for 52 years and would rather it be a memory.

Thank you all for the comments

Tom

ps. I did talk to JT today to order replacement threading gears. He suggested removing the anti-backlash springs. I plan to do that shortly. I losened my x axis nuts yesterday and the cranking is easier but there still seems to be loosness problems. Milling today the table was literally jumping in and out in y and maybe up and down. I'll probably have to get into all axis anti-backlash.

[salzburg]

There are hundreds of square wave generators on the net that you can
build yourself for under $ 20.00. I did. You plug one of those into your
Gecko and you got your powerfeed.

[sch]

www.surpluscenter.com has a wide variety of gear drive 24vdc in the $10-20
range. website http://ixian.ca/gallery/pwm/pwm.htm
has a write up and simple PWM driver for same. A good bit cheaper and not much harder to wire up than Geckos and Nema 34s.

[mixdenny]

Adapting a drive for a Bridgeport is very straight forward on the older Shoptasks, I'm not sure about the newer ones. Here is how I did it. Dennis

power-feed

[TomB]

Originally Posted by mixdenny Adapting a drive for a Bridgeport is very straight forward on the older Shoptasks, I'm not sure about the newer ones. Here is how I did it. Dennis power-feed

I've decided to go with steppers and gecko controllers. I've been hunting for why my table is so hard to move and have found that the lead screw is bent. Once I fix that I'll order the steppers and related stuff.

I can see how the Bridgeport drive would go on the y-axis, the TriPower is almost exactly like your's except the back plate no longer hooks to the table so the T-nuts are not blocked. But I can't see how to put a Bridgeport motor on the x-axis without a bit of modification. Both cranks get in the way and there is nothing solid like the plate to mount things to.

But thanks for the information and the pictures were very interesting.

Tom