A powered Z-axis for my bench top mill

[jariou]

I have owned an Industrial Hobbies mill for about 10 years. It is pretty big for a bench top model. It weighs over 800 lbs, has a big table, and a square column. I cringe when I ask it to mill somewhat hard steel but otherwise, for most of my projects, it is doing the job.

When I got it, the previous owner had put a 3-axis DRO on it which makes it a pleasure to use. Not long after I got the mill, I got an X-axis power feed from Harborfreight for a song at one of those parking lot sales. This was apparently a returned/opened item and I expected to find a problem when I would start to use it. But no, I set it up without problems, and have been using it without a hiccup since.

All of this to say, I've been pretty pleased with my mill from the beginning. It is not a Bridgeport or a Deckel or a Schaublin but it does the job. However, I can't stand the mechanism to raise the head of the mill. You need to turn a crank on the left side of the machine, and the ergonomics are all wrong. I hated it from the moment I started using it. I would rather change R-8 collets 3 times by hand than raising that head 1/2" up.

So, I cobbled together a motorized Z-axis as an exercise in "self medication", on the advice of my therapist! ;-)

I will present the problem and the solution in this thread in the days to come. I also have plenty of pictures to accompany the narration.

I hope you will like it.

[sewingmachine]

I bought a PM932 a while back and found the same problem. I took off the crank and mounted a small gear reduced DC motor with a couple of sprockets. I also mounted a micro limit switch for the top stop and a micro switch on a slide for the lower stop.
This works great and I can go from chuck to collets in no time at all.

Dave

[lugnut]

A friend gave me a motor from a hospital bed, some time back and with a little remodeling of the gear reduction I adapted it to drive the Z of my table top milling machine. I had to mount it on a angle to match the manual drive. I use a selector switch to select UP or DOWN and a push button to run the motor. A small grooved belt drives the manual crank. Sure saves a lot of cranking.

[QSIMDO]

I have the same machine and probably the same vintage.
I describe it as "a machine that will perform rudimentary milling operations" rather than over-inflate it's capabilities.

My attempt at powering the Z axis is sitting in a box as a reminder to check the specs closely when purchasing a gear motor.
Got all my parts assembled and mounted and nothing happened!
Well, it WAS working but imperceptibly as the motor output is about 1 rpm.

Rather than pay the price for a correct motor I mounted a gas cylinder and it works extremely well.
Rated at 200 lbs., cranking up is fantastic..cranking down needs a stronger effort but life is like that, eh?

[BCRider]

Fill the usual cavity in the head up with some heavy mixture to equal out the effort needed? The added weight might also make the machine less prone to chatter.

[jariou]

Sewingmachine, that was my first idea too. However, the motor I had at the time was bulky and I tried to build something simpler and strong enough. I thought of driving the Z-screw directly. So I climbed on top of the bench to look at how I could interface with it.



It is not so obvious from that picture, but I saw salvation! ;-) I took out the screw and devised a plan to drive it from above.



I figured I could machine something that I could press in that center depression and have the necessary features on that part to interface with the motor I had at hand.



So I also took off the screw carrier from the mill and machined a piece of nylon to register the motor's axle loosely concentric with the screw. You can see the result here but don't look in the hole quite yet, you might guess what I did next. Notice that I machined a flat on the piece of nylon to match with the motor enclosure that will find its way on top of my mill shortly.



The rumor mill is going and bets are open! What kind of motor will be used? Take a stab in the dark or an educated guess! ;-)

[QSIMDO]

Fill the usual cavity in the head up with some heavy mixture to equal out the effort needed? The added weight might also make the machine less prone to chatter.

Yup...about 2300 lbs. worth of new Acra is going to solve the problem!

[BCRider]

Yup...about 2300 lbs. worth of new Acra is going to solve the problem!

Well, I suppose that would be ONE avenue..... I'm just wondering how in hell you're going to cram all that down into the head of the bench mill.....

[jariou]

Let's keep going, we are now building an enclosure for the motor powering the Z-axis. Here is a first iteration at the layout of the components.



With a component of the system now:



And more layout and holes drilled to fix the other components:



And now with the previous component mounted.



I think I reached my limit of 4 pictures for this post. No idea what the motor is? Anyone?

[RichR]

I think I reached my limit of 4 pictures for this post. No idea what the motor is? Anyone?

Yeah, I recognize that gear assembly. You're re-purposing an electric garage door opener.

[jariou]

Yeah, I recognize that gear assembly. You're re-purposing an electric garage door opener.

Bingo RichR! You get brownie points! Someone is following!

So now that the "mystery" is over, we can go on our merry way and complete the work. The following pictures show how the nylon ring I turned is used to preserve concentricity between the driven axle of the garage door opener and the screw axis.







However, the real question is what is going on inside that ring? How can the sprocket and the lead screw be made to mesh?

[RichR]

However, the real question is what is going on inside that ring? How can the sprocket and the lead screw be made to mesh?

Pins that sit in the valleys between the sprockets teeth?

[jariou]

The answer is with a shaft coupling of course. At least that's how I saw it when faced with the problem.

It was easy to set up the sprocket to rotate more or less concentric to the axis of the screw. With its eight "fingers", it seemed to be begging for something to lean against. So I turned a piece of steel that would press in the top of the screw shaft. It extended another inch or so above the top of the screw at a diameter slightly larger than the sprocket. I then drilled eight holes around on a diameter that would create solid interference with the sprocket teeth.

Here is a view of the part.



And here are the pins.



Here is another view with the pins assembled on the "coupling".



A few observations are due here. First,you can see that I went out of my way to knurl the pins and the part of the coupling to be pressed into the screw. It was one of my earliest projects involving press fit and I just wanted to make sure nothing would start to slip in usage.

However, it turned out that the pins where a perfect fit without the knurls so I just pressed them upside down. The coupling itself fit very tightly with the knurls but would have been a bit loose without. So, as an insurance policy to allow me to be able to separate it from the screw, I had it drilled and tapped through. So that bolt just behind it is not there just to look pretty, I had tested it as screw jack and it did its job admirably.

And here is one last picture showing the fit of the pins around the sprocket.

[jariou]

Shoot RichR! You stole my thunder! ;-)

[QSIMDO]

Got a video of it working?

And did you keep the remote capability?
Could be dangerous though if a spurious signal set it off while you're working.