Diagnosing the Sieg 7X Motor

[RotarySMP]

Hi Guys,

Yesterday while making my ER32 Collet chuck holder I think I have done my motor some damage.

I was turning steel at about 75mm diameter (3") cutting 0.2mm depth of cut at about 450RPM and 50mm/m with 0.2mm nose radius TCMT carbide when the fuse popped. The next fuse popped as soon as the motor rpm was selected (motor unloaded). I could turn the controller on and off, but as soon as I sent popped to the motor the fuse blew.

I had already turned the work down from 80mm diameter so the machine had been working hard for about an hour.

The motor body was too hot to touch.

I removed the motor. The motor doesn't smell burnt. Neither lead has shorted to ground. The resistance between the leads is 17 Ohm with the motor stationary. Rises rapidly with the rotation.

The motor generates voltage when the shaft is turned.

Any ideas what the problem could be? and the solution?

[dkowalcz]

Hey Mark, good to see you...

The control may be toast. I've got a spare lying around that I can ship you if you need one.

This horsepower problem plagued me for ages until I broke down and got the "real McCoy"

Buy one of the surplus treadmill motors and an industrial speed control. Here's where I got mine, and a pic:

http://www.surpluscenter.com 2 HP 130 VDC 3210 RPM MOTOR
Item# 10-1906 $79.95 (you can get cheaper on eBay if you shop)

http://www.mcmaster.com 7793K12 Speed control 10A max (with heatsink)

I'm using the old headstock casting that has no gearing - on yours you'll probably want to pull the weird timing pulley that they use and slap on a regular XL series.

Couldn't tell you the speeds and feeds off the top, but I'm not at all disappointed with the power for shooting steel - I run out of insert before I run out of power since I'm not using flood coolant anymore. I'm doing mostly 3/4" and under bar work in 1018 and 304/303.

[dkowalcz]

Forgot to mention - the motor is DC so if you hook up a 12V battery it should turn at a leisurely pace... Might want to pop the brushes and have a look, make sure the springs haven't lost temper.

[RotarySMP]

Hi Dave, thanks for the offer. I live in europe, so my machine is set up for 230V.

I have a 1/2HP three phase motor and Siemens VFD on my mill, and might end up having to go that path. Bummer would be I would need the lathe to make the bits to convert to a different motor...

I have been working with two other guys (one here, Pierre from Belgium, and Sean from the States) and we have just about finished out three sets of conversiosn stuff to convert to ball screws. I was going to strip the machine down, to the motor pulley and finish my enclosure when I had the last parts for that conversion.

I already have bought some steel pulleys and a belt to replace the crappy chinese ones. Need the lathe working to bore them to size I just tossed out a 230V to 110V transformer which I could have used to rig up a one speed drive!

I have already checked the brushes and they are about half worn. The copper commutator looks to have worn about 1mm already.

I was just thinking of the 12V PSU I have lying around. I'll give that a try.

Cool you have two AXA tool posts on your lathe now. Can you post any other pictures of how you lathe is now? Why do you have the six lobe spindle encoder?

[RotarySMP]

Five minutes later...I just hooked up the 12V PSU and the motor seems to run fine in both directions, so I guess you are right about the controller. Do you know which bit normally dies? I can't see any off the obvious signs of electronic death, and it also doesn't smell bad.

I have just done the MOSFET resistance checks as detailed on http://www.littlemachineshop.com/Ref...leshooting.pdf and the 50 Ohm values ar3e the same, but I have 300K Ohms where I should have 120-140K Ohms on both mostfets. I wonder if those values are only for the 110V controllers, or if it is the same for the 230v?

10 minutes later.....
Cool, a self repairing system!!! I just hooked up the controller to motor and everything works again, PFM!

I guess there must have been a bit of swarf int he works causing the short somewhere.

At least I have learnt that the MOSFET values on the LMS chart are not the same as the values for a 230V controller.

Sorry to bug guys!

Dave I'd still like to see more pics of your lathe

[dkowalcz]

Ahh, yes, 230V. Forget it then, there's no way my old control board would work... The speed control I linked can do 230 or 115 though (there's a switch).

So yeah, the 7x10 mini is still mod central in the shop. Check out these better pics - I scored a big pick and place machine for the cost of a forklift rental and a buddy with a truck. 4' square table and linear motors, 12" under the head. It's so fast it's scary, alhough I don't have it under computer control yet (gotta mod TurboCNC to handle a 10V analog control loop).

The master plan is to use that as a load/unload robot for 3 7x10's at once; I designed a gripper with thru holes for air and coolant so it can take over my job of standing there with a can and a chip brush advancing the rod and putting parts in a bucket.

I milled the clapped out dovetails off the slide and replaced them with THK linear slides and a ballscrew. This is an order of magnitude better than the old setup, even with only two big 20mm trucks instead of 4. I've got some more on the way for the Z as well.

As you've noted I've doubled up on toolposts - it's easier to have two so that I can swap tooling front and rear willy nilly. I made some gang tool blocks for end drilling and stuff, so that's working out well. The old rigid rear cutoff bolted to the slide worked, but it was too inflexible.

The six lobe encoder is for researching improvements to TurboCNC - you can see in the pick that one lobe is "long" - that's the only one that TCNC reads right now for G33/76. I want to program a rigid tap cycle into the software, so the extra lobes are for A/B channels to pick off the position more accurately. It'll save me a lot of work to have the machine do the tapping.

Some of these pictures are a bit old, I don't want to wake up the wife yet by going into the garage... That orange robot is an early foray into the same thing, I'd be using that right now if I hadn't found the P&P.

[phantomcow2]

Hey Mark, good to see you...

The control may be toast. I've got a spare lying around that I can ship you if you need one.

This horsepower problem plagued me for ages until I broke down and got the "real McCoy"

Buy one of the surplus treadmill motors and an industrial speed control. Here's where I got mine, and a pic:

http://www.surpluscenter.com 2 HP 130 VDC 3210 RPM MOTOR
Item# 10-1906 $79.95 (you can get cheaper on eBay if you shop)

http://www.mcmaster.com 7793K12 Speed control 10A max (with heatsink)

I'm using the old headstock casting that has no gearing - on yours you'll probably want to pull the weird timing pulley that they use and slap on a regular XL series.

Couldn't tell you the speeds and feeds off the top, but I'm not at all disappointed with the power for shooting steel - I run out of insert before I run out of power since I'm not using flood coolant anymore. I'm doing mostly 3/4" and under bar work in 1018 and 304/303.

So you are satisfied with this external motor setup then? I have been getting very tired of the controller and especially timing belt setup of the mini lathe. Been considering using that 1.5HP treadmill motor and be done with it

[RotarySMP]

At this rate your lathe is going to end up looking like Stevie's cheap drill press converted to a mill. Maybe the headstock will still be used

What stuff do yu make on your lathe? I think the longest production run I have made on mine was 12 small simple parts, or two larger more complex parts. Still the conversion has been fun.

[dkowalcz]

Hey Mark!

I've been making all kinds of spacers and standoffs mainly, some special driveshafts, RC car dogbones, custom fasteners, bushings... It's been neat. My shortest run has been 25 parts, most of them 300 to 1000. Hence the motivation to put together a "babysitter robot" and bar-puller finally.

Some of the cycles are as short as 16 to 20 seconds, so figuring that it takes another 8 to 10 to grab the part off, slide more bar in, and hit go means 120 parts an hour. If I catch my breath a bit, measure them, tune the code etc, it's 100 parts an hour, so 1000 takes a hefty 10 hour day. Gets old quick...

Phantomcow - the treadmill motor torque is just right for the XL series timing belts. I'm very happy with it, I remember baby-ing steel with .004 depth of cut on the original motor... Very time consuming that way. Aluminum and plastic it's not so bad.

[RotarySMP]

I hope it gives you the income to retire and become a full time programmer Dave

Do you find you are breaking other parts of the lathe with the 2HP drive? I think you might be right about the brush springs loosing thier temper. I put the machine back together and ran it for about 10 minutes and then the fuse popped again. I could hear what sounded like arcing from the motor as it popped. As I removed and checked the brushes for wear and reinstalled them before testing the motor yesterday, the brushes had probably reseated giving me normal values.

[Trapper14]

wow dkowalcz exactly what I was looking for! Do you single point with that setup. I love the robotics thing you have planned there! Right now I am swapping out the spindle in favor of a larger one, with new bearings. I am one of the collaberators of Mark's. Sean

Why haven't you made some sort of bar loader, and the just have a slide come up to the spindle to take the parts away? Thats how the indutrial lathes at work run CHNC II's gosh I love watching them running. They are basically a hardinge toolroom lathe CNCed

on more than one occasion I ahve found myself day dreaming while reading yours, and marks pages lol

Sean

[RotarySMP]

Hi Sean,

Have you got your treadmill motor yet?

Dave K is the author of TurboCNC.

A bar feeder is probably not worth the effort if you still have to turn the chuck key. Moving the bar is not the big deal, for multiple parts you just position the tool holder to act as a stop, loosen the chuck and push the bar through. It is the manual chuck that kills you.

A bar feeder would be better on a machine running a native 5C collet spindle with collet closing lever. Then you could hook up a pneumatic cylinder to run the collet closer and bar feeder for you.