College Engineering do a casting for a slotting tool….if that helps? ( I happen to have one, its on my roundtoit list..)

Andrew – whereabouts are you? I'm in West Gloucestershire and there is a slotter in my shed. Alternatively if you bore them and post them to me I'll slot the keyway and post them back Best Pm me if you're interested rgds Simon

I had a similar problem to make a keyway in a bushing I made for a pulley when fitting 3-phase motor to my VMB. The bushing us loctited into the large bore of what was the intermediate pulley and fits the 3/4 shaft of the motor. (The pulley normally has two large ball races and runs on a stud.) I turned and bored the bush in mild steel, and at the same setting locked the headstock and mounted my 5/8 boring bar which has a dedicated mounting block on the topslide, replacing the normal Dickson holder. I made an HSS tool bit to a sort of parting profile and fitted it to the end of the boring bar at centre height, but at 90 degrees to normal orientation. Then used the rack to move the tool back and forth to cut, applying feed from the crosslide. It took a while but did the job without needing to make any special tooling (other than the cutting bit). I must have been lucky profiling the tool as the slot needed almost no fettling to fit the key.

The design for the casting College Engineering sell works well. The centre height comes out correct for myford 7's. I use one on a Boxford but it needed packing up on a spacer. The fact that they match the centre height of the lathe is a good idea really. Some make things up to fit in a toolpost. The principle is the same on most of them really. A shaft that fits nicely in a hole on centre with the lathe and a lever arrangement that stops it rotating and provides the cutting force that is needed.

Using the rack feed etc on the lathe to do it can be a very bad idea – something is likely to break.

Can't find a photo of the one based on the casting as lots of people fabricate them. Few shots here

**LINK**

Also some on youtube.

John

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I reckon the gear that ran along the rack on my Raglan was broke doing it that way Jason. I've heard from others at times that have had this experience.

Maybe this is one up for China and down for Myford and Raglan.

John

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I do not know the size of gear or slot you are talking about but I have used a very simple adjustable broach to make slots for pulley and gear. More details are here:

http://mikesworkshop.weebly.com/small-hole-slotting-tool.html

Mike

Andrew,

I'm over on the Notts Derby border NG10 post code so not that far away if you want to pop over and I can broach they whilst you wait, only a 10 minute job.to do the lot.

Andrew,

I made a slotting attachment for my lathe some years ago and have used that to make keyways when needed. It bolts to the cross slide instead of the topslide.

Thor

Maybe Neil will throw up a freebee. The design that uses the College Engineering Casting was in MEW Aug/Sept 1991. The casting doesn't look much different to the one I have which I thought was much earlier.

The basic idea is that when the base has been machined the bore for the ram can be done by mounting the casting on the cross slide. That way it's exactly on centre and it's possible to slot keyways that will have a very sexy fit pretty easily. The problem with the hole and file idea is getting the hole on a true radial position. The keyway usually finishes up somewhat wider than needed, width depending on the skill of the person that does it.

I used mine to gash an RMS thread tap. Fine for that bit getting a sharp edge after screw cutting it needed some delicate dremel grinding. In the end I bought one but it worked well in brass.

John

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I wouldn't claim to be a filing expert but I had no trouble doing sufficiently good keyways in my change wheels for threading duties. Helps that the Smart & Brown uses a small key and relatively thin changewheels. Be different if taking real power or cutting large keyways. If I ever do a metric set for my Pratt & Whitney Model B I will be sorting out a bit of mechanical help.

Even if you have a slotting head putting a drill in first makes the job a lot easier as the drill takes most of the metal out. If you don't have a slotting head and don't see enough work in future for making one to be worth the time and effort Jason's second picture is probably best approach to final finishing after opeing the drilled hole very close to size with a file. I'd probably have done mine that way if I'd had a suitable piece of tool steel in stock. Drilling first also reduces the load on a broach if you have a set.

Clive.

Yes, it pays to bear in mind that change gears are a low-speed, low-power application so keyways do not need to be a super precision job. Even if they turn out a bit of a loose fit, the slack in the gear train is taken up as soon as the tool starts to cut and so is consistent, regardless of clearances between gear teeth or keys.

On my old Drummond the changegears are not keyed but paired with taper dowel pins that are a press fit in one gear but stick into a clearance hole in t'other with 10 thou or so clearance, so there is all kinds of operating slop but they have been cutting threads for 80 years or so without problem.

It's a different situation if for instance you are cutting a keyway in a dividing head gear train as I was. In that case you need precision location for most foolproof action so a machined keyway will be best. Ditto for say a motorbike crankshaft key that is to handle 20-100 horsepower etc. Any slop there would result in failure.

I made a Slotting Attachment using the College Engineering Supply casting. (It came with a reprint of the article by, the now late, Peter Robinson. He was a member of the Peterborough Society of Model Engineers)

Once the base had been machined, mounting it on the Cross Slide of the Myford, allowed the bore for the Ram to be machined. When the Myford was sold, made a riser block to adapt it to my BL12/24.

When a one off square socket (for a speedo drive adaptor for a scooter) was needed urgently, the tool was gripped, axially, in a collet, in the Tailstock and racked too and fro using the Tailstock Handwheel, with the Tailstock clamped to the bed. Progress was slow, each axial cut was only about 0.010" deep, rotating the chuck holding the workpiece 90 degrees for each cut. It took time, but eventually produced the required square hole 1/2" deep.

So, if you are wary of filing the keyway, that is another possibility. But putting on the cut using the Cross Slide (as already suggested) would be my preferred method.

Howard