Keyway Broach Bushing - thinking outside the box

[SamI]

So I've had a job I've been putting off for a few days while I wait for a keyway bush to be delivered. When it comes I discover that a "Type B" metric bushing is not compatible with a "Type B" imperial broach! It seems that over here in the UK imperial bushes are hard to come by so I decided to go ahead an make my own.

Ordinarily this would be a straight forward project however I don't have a mill and as we know lathes aren't very good at making things that aren't round so I needed some out the box thinking (although it's probably fairly standard practice for some of you guys!).

I have milled a few things in the lathe before however these have been small enough to fit in my tool post. In this instance the bush was too large to fit. Also, the slot needed to be bang on centre which I have found int he past to be very difficult to achieve in the lathe without a milling attachment for the cross slide.

I started off turning some bar stock to 16mm which fit in my toolpost.



I needed a way of getting it back into the toolpost in the same position later so I started by milling a flat in the bar.



I know holding an end mill in the 3 jaw is less than ideal but it's what I have. I do intend on getting a collet chuck soon but until then I'm stuck using the 3 jaw (and I couldn't be bothered getting the 4 jaw out of hibernation for this!).



I then turned the bar round with the flat up against the back of the tool post and milled a 60 degree groove along the full length.



And then drilled and tapped 2 M6 holes (the phone went on charge at this point and wouldn't reach the drill press so no photo's I'm afraid)

I then cut a section of 19mm bar that just so happened to fit the bore I was trying to broach perfectly. I drilled two holes in here to correspond to the two I drilled and tapped in the grooved bar.



A note to self - get the correct size drill for bolt clearance! I didn't have one to hand so ended up only using one bolt to secure the piece. It worked fine but it was still frustrating to make a schoolboy error like that!

Next I mounted the soon-to-be bushing in the toolpost by bolting it to the grooved bar. I then milled the slot. I was actually very pleased with how this turned out. sure there was some vibration in the machine but the finish was better than I'd hoped for.





I then parted off the excess and faced to the length of the part to be broached.




A few things I have learned here

* I need to take my time more when marking out - some of my problems with the bolt holes aligning were due to me not re-centring the work under the drill press when changing between the grooved bar and the bush.
* A broaching bushing should be longer than 20mm! I found that the broach would start to tilt and cut an angled keyway. I switched out to a 40mm long bush and this seemed to fix the issue.
* When the above happens, DON'T back the broach out of the hole. It will chip teeth! Try and force the broach back into alignment and proceed slowly.
*Don't try and drill a hole in the top of your home made hydraulic press in the drill press! I couldn't find any suitable packing so used bricks to get it to the desired height. These were no where near sturdy enough! Admit defeat and go use the hand drill!

All in all it was a fairly successful project and I hope that others may find this useful. It was only out of necessity that I even considered making this in the lathe and until very recently I considered broaching to be something that couldn't be done affordably in the home shop.

 

[mikey]

Pretty ingenious approach if you ask me. Sometimes we just have to make do and what matters is that we get the job done. I liked your "lessons learned" segment - thanks for sharing.

 

[NortonDommi]

Nice job. I'm am not trying to be rude but I thought it was obvious that Metric and Imperial sizes of keys, broaches and broaching bushes were all different. About the only interchangeable things are the shims. Surprising that you have any difficulty in the UK getting Imperial stuff . Mind you if everything was straight forward you wouldn't have delved into what you did so now there is another notch on your stick.
Could I ask you to do one thing though and that is get that ring off your finger. Jewelry of any kind has no place around machines. I've seen some horrific injuries over the years and a finger getting torn off because of a ring is one of the worst. Watches with metal bands getting welded into bone is another you can't unsee.

 

[SamI]

Nice job. I'm am not trying to be rude but I thought it was obvious that Metric and Imperial sizes of keys, broaches and broaching bushes were all different. About the only interchangeable things are the shims. Surprising that you have any difficulty in the UK getting Imperial stuff . Mind you if everything was straight forward you wouldn't have delved into what you did so now there is another notch on your stick.
Could I ask you to do one thing though and that is get that ring off your finger. Jewelry of any kind has no place around machines. I've seen some horrific injuries over the years and a finger getting torn off because of a ring is one of the worst. Watches with metal bands getting welded into bone is another you can't unsee.

I had wondered about the compatibility of the bushes. I couldn't find any information at hand but I had hoped that the "Type B" sizes would all be the same and it was the width of the cutting teeth and depth of the broach itself that differed.

Thank you for your warning. I am well aware of the risks and I do try to remember to take it off when I enter the workshop. More often than not however I forget (as you can see). The main reason I take it off is actually because coolant gets under it (along with chips if I'm really lucky) which causes skin irritation which can cause discomfort for days. I will see about getting a small tray near the entrance of the workshop to put it in. Would be handy for keys and other random pocket junk too! Hopefully having somewhere to put it that's visible will help to jog my memory.