Power feed for a benchtop mill

There are lots of vendors supplying their variations of mills based on standard components produced, and usually assembled, in China. These are excellent value machines, and the few I have used I have found to be quite capable.

The power feed solutions available for the X-axis are all pretty much the same. It looks to me like a power feed design, from many decades ago, has been replicated and then very basic solutions used to adapt the fitting of that design to other mills.

The original product looks like it was designed for a large floor standing Boxford knee mill. This is not ideal for a benchtop mill and none of the attachment methods that I have seen are quite right for my requirements. Therefore, I have designed my own bracket.

I have a Warco WM18 mill but my design, or a slight variation of it, probably applies to similar mills marketed by Chester in the UK and Precision Matthews in the US among other vendors.

Position

The main requirement I was trying to solve with my solution was to mount the power feed so that it does not foul the bench or the chip tray of the mill, while also not requiring too much bench real-estate.

The fitment for benchtop mills provided by all the versions that I could find use a horizontal bracket held by a rather disappointing looking pair of bolts clamping that to the mill table. The power feed sticks out a long way, usually to the left of the mill table. I did not have enough space for that arrangement.

I briefly thought about designing and building a solution from scratch, using a stepper motor, but the dog clutch needed to instantly stop the feed made this unlikely to be significantly better than the off the shelf motor with the clutch and controls built-in. I therefore concentrated on a better method to mount a readily available power feed.

For inspiration, I looked at the way a few others had mounted the feed and concluded that I would prefer to replacing the left handwheel and have the power feed motor horizontal, but facing the front.

Typical advert on eBay

Having made that decision, I bought the standard kit intended to hang from the right handwheel of a Boxford mill.

Mounting

My design fits to the left hand end with the bronze gear between the motor and the table. This is the opposite of where it would fit on a Boxford mill.

3D printed mockup

I designed and 3D printed a couple of possible brackets to bolt on in place of the original end bracket. The result was a bit too large to mill out from a block of aluminium so I opted to weld together some 15mm thick steel plate.

This mounts using the original M6 threaded holes and the holes for the 6mm dowel pins.

My mill has a DRO scale mounted on the left hand side. I adjusted the bracket to maximise the movement of the table, but my design does reduce the table travel by about 50mm. I could probably gain a further 15mm if I moved the DRO scale, but for the moment, I don't need that travel.

Gears

The main bronze gear is supplied bored for a 16mm shaft. The newer WM18 mills, such as mine, have a 17mm shaft with a 5mm key.

I found it fairly easy to mount that gear in the lathe and enlarge the bore. I also pressed in a 5mm keyway.

At a later time during prototyping I cut 15mm off the length of the gear.

I also cross drilled a 5mm hole and threaded for an M6 grub screw.

I bought and used some 17mm ID shims to help position the gear, but these are probably redundant with the grub screw.

Bracket

As mentioned, the larger bracket is made from 15mm and a small length of 6mm mild steel plate. The end mounting plate which the motor housing is bolted to, is made form 6mm steel plate.

Inevitably, the design evolved slightly as the prototype progressed.

I originally had a bearing in the design, but I have eventually opted for a ball oiler instead. That is in keeping with the rest of the mill. I also had to mill a clearance slot for a stepped radius on the bronze gear, that was just a fraction larger than I had initially allowed for.

On the largest section I drilled the mounting holes on the mill, before assembly. Also before assembly, I faced one side on the lathe and bored out the hole for the shaft.

My welding leaves a bit to be desired, but it's more than strong enough and I've been able to clean up most of it.

As welding inevitably pulls the assembly out of alignment, I've used the mill to get to the final dimensions.

Alignment

The last job was making sure that the motor axis aligned correctly with the shaft.

I made a bush to fit with a 17mm ID for the shaft and a 24mm OD to fit the motor mount spindle.

Sketch of the bush

With the bush in place on the shaft and the end plate attached to the motor mount, I held the motor in place on the shaft and square to the bracket while carefully transfer punching the mounting holes.