Ideas for (re-)mounting a mill dial

I'm in the (ongoing) process of CNC-ing my mill and it's looking exciting!

I've ended up with double ended NEMA23 stepper motors, because (sensibly or stupidly, who knows), I still want to be able to turn the leadscrews by hand for delicate bits (lest I destroy my CMD10 micro mill gears AGAIN!).

I'd like to be able to remove the dial/handle when CNCing so I don't get caught as it spins.

The existing dials are nice enough, but have an 8 mill centre with a 3mm keyway.

The stepper spindle is 6.35 mm. In my head I have three options none of which I like.

I can try and make a sheath with 6.35 inner diameter and an 8mm outer with a keyway milled in the stepper spindle and the sheath. This sounds tricky (0.8mm wall thickness?).

I could make an extension with one end 6.35 inner and the other end 8 mil outside (with whatever keyway and stuff I need) , but that will stick out even further than the current motor assembly.

Or I can make a new dial with an appropriate inner diameter and a grubscrew or something. Which is fine, but then I'd need to engrave markings on it which is quite a bit of work (and I'd likely mess it up).

Usually when I ask a question like this I get 20 better ways of doing it. here's hoping!

Iain

Iain,

Wouldn't it be simpler to bore out the existing dial (handle?) to say, 12 mm, turn a sleeve to fit and secure with Loctite or similar, then drill to 6.35 mm to fit the stepper motor spindle. (6.35 mm sounds suspiciously like ¼ inch to me.)

John

Edited By John Hinkley on 12/05/2016 17:35:45

If you are intending to use Mach3 then get a pendant with a mpg on it. You will not need to turn the steppers manually. There is also a risk of generating pulses of electricity in the electronics if you turn the motors manually with them connected to your controller, think magneto here. If you want to use handles give some consideration to an easy way to disconnect the motors.

Martin

I've been manually winding the feed on my miller without disconnecting the stepper for years, never caused any problem

HI, John. That sounded like a good idea, but when I check the dial / handles, they are mainly plastic with a 14mm brass insert with the 8mm bore in it. boring out to 12mm is probably not practical.

On the other, I discovered that the indicator dial actually comes off, which means I can go with plan 3 which is to lathe a new handle and to use the old dial.

Frances - I did look at the link in your other post and stole was inspired by some of the ideas. I'm actually running the steppers inline through an aluminium coupler bought for a couple of quid from eBay. It seems to work well. Having said that, half the fun is assembling what you want from the bits on hand - I'm a long way from finishing off the project (if I ever do) so am approaching it piecemeal.

Martin - I'm writing my own software for now, but may use GRBL later (it's an arduino controller). I've got some rotary encoders coming which I may press into service, but I felt I wanted to have the 'feel' of the mill if I needed hand control.

Duncan - good to hear that manually winding should be OK. My motor controllers cost about £1.29 each so if I blow one up I'm not going to cry!

Iain

It will probably depend on the type of driver you have, if you leave it connected. I find that the common 2M542 drivers, even if unpowered, completely change the feel of the stepper if you drive it by hand as the commutating diodes charge up the reservoir capacitors. Even if you disconnect the stepper from the driver the "feel" of the handle will be quite different. I think MPGs is the way to go.

Never tried it myself but I believe if you connect 2 stepper motors together (connect corresponding colours from each motor together), you can drive one by turning the other, with no other components involved. Aha - here you go.

You'd need to spin them pretty fast to generate enough voltage to damage the drivers. Putting it another way, you'd need to spin them faster than their max unloaded speed when driven by the driver, at which point the back emf equals the power supply voltage.

On my Bridgeport CNC conversion, I've also retained the original handwheels on the leadscrews although the motors drive through reduction belt drives so it was easier. I plan to shorten the handles though, given that they are at the same height as my knackers and are planned to spin fairly quickly and suddenly. MPGs sound fine on the face of it but you need to power everything up before they will be of much use to you.

The only difference I notice is that the rotation is 'notchy', it tends to move in 1/2 thou increments (200 step motor on 0.1" pitch leadscrew)

Iain, where do you get a motor controller for £1.29? Mine came from Motion Controls and cost a LOT more. Is it bi-polar?

Hi Iain,

For the X axis could you add the stepper motor to one end of the table and have a winding handle with a folding handle on the other end?

Similarly could you have a folding handle on the Y axis but attach through the motor as per one of your ideas? There are flexible shaft couplings with step-up/step-down shaft sizes.

Ed.

Hi, Duncan,

I was, erm, exaggerating a bit. This is what I bought at £2.50. Searching today, I found this bringing the unit price down to under 2 quid (and with heatsinks!).

The board will handle up to 1.2A without heatsink and 2.5A with heatsinks. Chip spec is here. It would be pressed to handle the NEMA23 motor at full whack, but it has current control and I don't need the full torque - a big NEMA 17 turns the leadscrews well enough at 0.6A.

It integrates very easily to arduino or raspberry pi - and probably most everything.

I admit that once you go above this spec you start jumping up in price quite a bit!

Ed - I'm both inexperienced and trying to minimise the work and costs. Attaching the stepper motor to the end opposite the handle (or the handle on the opposite end to it is currently) is more than I can deal with!

I think this would be easier if the leadscrew stayed in place with the nut moving (like a lathe). But on my machine the nut is fixed on the lower axis or body and the leadscrew moves - if you see what I mean.

Iain

That's what Andy Pugh did on his Harrison conversion - on the X axis at any rate. The leadscrew doesn't rotate which looks weird - the ballnut is mounted inside the toothed (driven) wheel and turns with the motor. He even had his own housings cast. You can see how the rotating ball nut arrangement looks at the end of this video.

Difficult to do this without losing some travel, particularly where the leadscrew brackets can actually move to within the extents of the saddle eg Bridgeports. Whether or not that's really a problem may be debatable of course.