Vice as Broaching Press

[Ian HewsonParticipant @ianhewson99641]

Hi

keyway is parallel, not on a taper, let us know how you get on with the two flywheel tapers

Ian

[JasonBModerator @jasonb]

The planing is usually done by moving the carriage so cuts parallel to the hole. Not sure if it could be done by turning the topslide handwheel which is quite small., though you could just save that for the last few cuts as the 1:100 taper is quite shallow.

I have seen the topslide converted to sliding action with a suitable lever but depends if you want to make tools or get on with the engine

Broaching just needs a tapered slot cut in the bush.

[James Hall 3Participant @jameshall3]

JasonB: Yes, just the very final cuts for the taper – at 1:100 could be very shallow and few cuts.

May be inexperience on my part but if broaching with tapered slot in bush wouldn’t this tend to put some sideways force on the broach – as now not supported along the length of the bush – and hence risk breakage. That’s academic for me, but interested for future reference.

[James Hall 3Participant @jameshall3]

Ian Hewson: It’s my understanding that a gib-key requires a slight taper in the DEPTH of the key – perhaps I expressed myself badly.

[Ian HewsonParticipant @ianhewson99641]

Hi James

yes, the key has a slight taper, slot is parallel to the bore. Found the tapered cone fixings gave me the best running flywheels that I have made, but that could just be my machining.

Ian

[JasonBModerator @jasonb]

James, the slot in the bush is tapered where the back of the broach and any shims runs against it so fully supported. This results in the slot in the hub being shallower on one side than the other which matches a standard Gib head key.

[James Hall 3Participant @jameshall3]

Jason B: I’m not arguing against your vastly more experienced explanation here, but it seems to me that the bush slot being tapered (as I assumed it would be) would obviously mean that some of the broach teeth would not be in contact with the workpiece (presumably all but the first one to start with, then an increasing number in contact until the whole taper was cut) so that the broach would, in effect be ‘unsupported’ on the workpiece side for the section where the teeth were not cutting. Perhaps, though, the couple produced in the broach by the resistance of the cutting teeth would tend to force the broach against the bush so that it would, in effect be supported. I’ll take your word for it that it works.

I’m attracted to the idea of a gib-key because to my mind it looks perhaps a little more authentic than tapered collets – though I may stand to be corrected. The chap here (https://www.modelenginemaker.com/index.php/topic,11005.45.html and scroll a long way down) uses them – though the appearance is then rather spoiled by a grub screw which he apparently feels necessary to hold the key in position. Could you advise me as to whether the functionality of a gib-key actually scales down so that it is secure when driven home at this size – and following that how likely would problems be in freeing it if ever necessary?

[James Hall 3Participant @jameshall3]

Ian Hewson: See my answer to JasonB immediately above as regards my interest in using gib-keys.

These would only be my fourth and fifth flywheels – so far machined for a Stuart H10 and Beam (3″ and 7″) flywheels with no appreciable wobble when running so I’m reasonably confident of getting it right when the flywheel fit on the shaft is the determinant. I’m actually fairly confident that I could tackle the job using the split collets though, of course, that does introduce an additional chance of things going out of concentricity – I note that Andrew Whale ran into difficulties with one of his flywheels using collets

[Ian HewsonParticipant @ianhewson99641]

James

The choice of course is yours, only trying to help.

Ian

[James Hall 3Participant @jameshall3]

Ian Hewson: I never took you comments as anything other than being helpful, and apologise if I have given any other impression.

As I gather you are building, or have completed, a Farm Boy, needless to say I would very much welcome your further helpfullness by hearing any tips or wisdom that you might have to pass on – I anticipate that this project will probably considerably tax my relative inexperience so any help will be most welcome.

[DalboyParticipant @dalboy]

I went with the tapered bushes on my flywheel and these were my first flywheels I did the bore as described on the plans then did the keyway before doing the taper and the bushes while I had the angle set so they all matched. I drilled the three securing holes before doing the tapers.

I found that I had no problems with it as per the plans

 

[JasonBModerator @jasonb]

James, even with a parallel keyway when you start the cut only the first tooth is in contact with the egde of the hole, the “lead” of the broach is not in contact so there is just as much uneven contact doing a straight cut as a taper.

It is only as the first tooth reaches the end of the cut that you have full contact which on our sort of size flywheels and keys may be 6-10 teeth and that is when the force needed to push the broach through is at its highest.

Sometimes I borrow a friends hydralic press which is really needed for the 3/16″ broach but below that I can get away with teh drill press but for 1/8″ I eill push the 3/32″ through first to make it easier on the drill and also my right arm. I put a block under the table on the drill as you can see a bit of flex otherwise.

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