Hello:

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This is a (sort of) followup to this post.

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I went looking and found what I had started working on (more than a year or so ago) while I waited for parts and assorted tools to continue with my U3's much needed rework, which is still in progress. Like a visit to your odontologist: you know when go in but not when you'll leave.

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What I had in mind was using the existing OEM accesory (that expensive little thingy ... ) but driven by an independent 12/24v DC motor with fwd/rev PWM control. A simple solution to the 'twirl around the handle' hassle involved in moving the carriage away when not turning with a tool.

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It would still use a belt (preferably round) but it would be of a larger size and section so it would (hopefully) not stretch or slip like the OEM spec o'rings used from the factory.

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The photos attached are just a proof of concept, a general idea to improve upon and share with the board.

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Notes:

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1.

The mounting plate for this mock up was made from scrap galvanised steel sheet.

The original one will be replaced with a larger one made from 4 or 5mm laser cut steel plate.

The final dimensions and shape of the new mounting plate will become clear when I know what the driving pulley looks like and the exact motor used.

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2.

This U3 accessory is notoriously difficult to take apart to clean and grease.

If you plan on taking it apart, have a close look at the exploded view I am attaching (from the U3 manual).

There are a few things that will be lost if you don't. eg: parts 9, 10 and 11

Don't ask me how I know that.

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3.

You may notice that the hole through which the knurled knob used to engage / disengage the power feed has been enlarged.

It has been done so that it can pass through the mounting plate by just undoing three screws.

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This is needed to be able to take the mechanism apart without having to remove a pin to then remove the knob to then remove the shaft and so on.

ie: to avoid all the hassle involved.

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But don't look for it in the exploded parts diagramme as it is not numbered.

You can see it to the left of the gear in the main axle.?

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Eventually, a thin rubber/silicone something can be put in place between the gear and the mounting plate if grease starts to come out while in use.

But if hard white/yellow grease (B&D power drill gear stuff) is used, it should not happen.

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Comments / suggestions welcome.

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Best,

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JHM

This is my way of having a power feed on my Uni3.

I found a small 24v motor with a 600:1 gearbox ratio. I made a variable powersupply "1.25v to 30v" and i can get the speed down to 19 revs per minute. It is reversable with an on off on switch. It connects directly with the lead screw with a simple slot in an aluminum adaptor. I simply slide it to the left when not in use. P.S. I have no idea where the 24v motor comes from.

Hello:

On Tue, Nov 26, 2024 at 10:32 PM, Mike Gidley wrote:

... my way of having a power feed ...

Nice job.

The OEM power feed attachment has a 40:1 ratio and the carriage screw feed advances 0.02mm / turn.

I still have to see what specs I can get from the motor I have to see if it will do.

ie: check the nominal voltage RPM / torque, do the math and see how variable the spec can be.

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No idea what voltage it runs at but it is probably 12v or less.

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One thing I have not mentioned but can be seen in the photographs is that for this modification to be viable, the U3 has to be put 'on stilts'.

Otherwise you cannot hang the motor under the PF pulley.

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No big deal as mountimg it higher makes it much easier to clean under it, otherwise it is a 30/45 minute chore with a rag and a toothbrush.

My U3 sits on hardwood blocks to give it a 65mm clearance under the ways.

It ended up being just enough, should have gone for a minimum of 80mm.

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Best,

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JHM

I've been thinking about a stepper motor based power feed for the Unimat for a while.

I'm also thinking about a second stage of the project to make a full electronic gearbox

by putting a rotary encoder on the headstock to track rotation.

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Are the group as a whole interested in me working on this and releasing the

electronic and physical designs?
I'm not sure I can justify the effort just for me, but it might be worth it if enough

of you are interested.

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Basically, a standard NEMA 17 stepper should be able to drive the leadscrew,

and I can print a coupler out of flexible filament for minimum backlash, together

with a mount mount design to go on the baseboard.

There are a few options for rotary encoders, and a modern microcontroller

like a Raspberry Pi Pico should be good for speeds up to say 600 rpm.

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For those who don't have access to 3D printers and the like, I may be able

to make partial kits.

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Thoughts, comments?

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Mike

Do you think this type of setup could be made accurate enough to single=point thread?

Michael,? I would be very interested to see what you could come up with I am just at the point trying to decide which way to go with a power feed for my U3.

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Regards

Phill

For the initial aim of providing a power feed I would just use a small battery screwdriver, or something a bit more sophisticated, depending on what I have in the junk cupboard. Coupling it to the leadscrew in such a way that the handwheel still turned freely when needed is the problem. However, I was also thinking about a rapid feed, following discussion about fitting a split nut to the carriage and adding a rack and pinion to the saddle (on a U3). On the bigger machines I sometimes use, this is done with a motor/gearbox having an adjustable feed rate, plus a "rapid" speed in both directions, all controlled from a single lever. When the lever is in the mid position the handwheel is free, giving a switch which could be described as (? )< 0 > (?). To get the free handwheel needs a clutch in the drive scheme. Apart from the five position switch, which is more engineering than electronics, the rest is simple enough. The fine feed positions latch, the rapid positions don't. On the U3, which already has provision for driving the leadscrew at the headstock end, it would not require much modification of the lathe. On the DB/SL it's not so simple. So I think a toothed/dog clutch would be suitable, maybe mechanically operated or electrically. I'm sure it would be simpler than the rack and pinion mechanism discussed before - that looked to me to be more of an exercise in design and machining techniques than a convenient solution to an occasional problem.

Hello:

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On Thu, Nov 28, 2024 at 02:08 AM, Keith S. Angus wrote:

Yes, I think I have seen similar workarounds.

The motors and gearboxes inside those things can be quite useful.

I have the idea that the split nut solution is complicated mainly because in the U3 the carriage leadscrew is not an ACME thread.

ie: not square

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The clutch on the U3 power feed attachment works well enough though and if you already have one or can get one for a reasonable price, the problem is solved, at least up to that point.

Very elegantly put.

What did call my attention is that, besides the example published by the author in MEW, in all the time I spent looking on-line for details on what it was all about, I did not come across anyone who actually built it. Maybe someone did but it was not posted/published?

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I made another more accurate mock up for the motorised version of the power feed I am working on, this time with the motor and power feed rotation axes properly aligned. This is essential as they are at 90° with respect to each other and the transmission belt will be used as in was before but on pulley driven by the motor instead of the U3 spindle.

(see attached photo)

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Unfortunately, I cannot recall where the motor came from and it has no markings.

It is the same same size as the well known RS-555-XX series but with no red mark indicating polarity.

This means it is bi-directional, I checked.

(see attached diagramme)

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It has a decent amount of torque and have tested it (no load) with a 12v/1.25A and a PWM regulator but have no means to knowing at what speed it is running with no PWM ie: 100% on.

My guess is that it will run fine under load with another 12v/3.50A I have in a drawer.

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Being a permanent magnet DC motor, it does attracts all te fine swarf around, so it is a problem.

Still have to find a solution.

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Comments and suggestions welcome.

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Best,

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JHM

There seems to be some resistance to using stepper motors, which surprises me.

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They are standardised, cheap, and easy to wire up with cheap controllers,

and can give repeatable positioning.

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Can anyone tell me what the problem is?

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Mike

For my taste, I just prefer regular motors.? On Sherline, I use their external motor.? The Cowells has a power feed/threading gear drive.? On the Maximat, you have regular gear feeds.? I have never bothered with power for either Unimat.? If I found a feed attachment cheap, then OK.? Ebay full price - no.

Hello:

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On Thu, Nov 28, 2024 at 10:41 AM, Michael Karliner wrote:

... some resistance to using stepper motors ...

In my specific case, I have five or six of these series rs-555-XX motors.

Two of them from some model of B&D battery operated screwdriver, complete with gearboxes.

That is why I am using one of those.

... standardised, cheap, and easy to wire up ...

... can give repeatable positioning.

Again, in my case, the modification of the U3 power feed attachment is to address the shortcomings I mentioned in a previous thread.

Be sure that if I need to do any CNC-like things eg: repeatable positioning with my U3, I will obviously look for a stepper motor.

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Best,

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JHM

On Thu, Nov 28, 2024 at 01:01 PM, Julius Henry Marx wrote:

Being a permanent magnet DC motor, it does attracts all te fine swarf around, so it is a problem.

Still have to find a solution.

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Put some sort of box around the motor, non magnetic, (aluminium or plastic). The extra distance away will reduce the magnetic attraction and it will be easier to clean the dust off. Use a sealed box so the dust doesn't get inside the motor and eventually jam it. There are some small aluminium drinks cans that might do the job, or a wide range of plastic containers like shampoo bottles. I've just chopped up a food container to protect my 3D mouse - not from dust - just to stop it getting leaned on occasionally. It causes chaos on the computer if the programme isn't expecting to be told to rotate the image in 3D. Took me a day to sort out the mess last time.

Hello:

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On Fri, Nov 29, 2024 at 02:34 AM, Keith S. Angus wrote:

... some sort of box around the motor, non magnetic ...

I was thinking of a shrowd, piece of aluminium tubing using ~3/4 of the circumference.

The thing needs its airflow.

... extra distance away will reduce the magnetic attraction ...

The motor is also relatively far away from the source of the swarf.

ie: down below, under the plastic belt guard.?

... a sealed box ...

That would be a tricky thing to achieve.

Space is at a premium there.

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I am looking into the possibility of (if space permits) changing the orientation of the motor's axis.

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Instead of being at 90° to the axis of the power feed pulley, both would be parallel and on the same plane.

That would do away with the twirly-twirling of the belt drive and simplif things considerably.

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This new position of the motor would have the benefit of reducing its exposure to swarf.

We'll see, a new mounting plate is still in the imaginary stage.

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Thanks for your input.

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Best,

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JHM