Machining a crank web

so i have just machined the 3mm disc required for jan ridders flame licker engine. I now have a 3mm disc ready to be milled to a crank web shape. How to hold and machine is s the question.

Edited By Andrew Cree on 14/10/2018 19:25:28

Which one of his flame lickers are you making and what tools do you have available as the crank could be filed or milled?

The plans as in model engineer 4323. Seems a lot to file. I have a warco 290 and sieg sX3 and a rotary table.

Edited By Andrew Cree on 14/10/2018 19:43:11

Myself I would make from round bar. face off and turn to diameter add any boss if needed then drill and ream the central hole.

Then over to the mill, locate ctr and then offset to drill and tap crank pin hole. If you already have a plain disc then hold that, locate ctr and drill ream that then do the crank pin hole. *

Saw/part off and then mark out the profile of the crank, this one is a bit plainer but same principal. Saw off most of the waste and then hold vertically in the mill vice and mill to your marked out lines.

Round any edges if needed and job done

I also like to leave my crank webs over thick so that once they have been fixed to the crankshaft they can by skimmed to finish thickness which also ensures that the face is true to the shaft and the pin will fit square so no binding.

* if the two flats need a fillet where they meed drill holes for that at this stage and later mill upto the edge of the holes.

Edited By JasonB on 14/10/2018 19:48:28

Many thanks for such swift response. Will need to modify your process as I now have a perfectly formed 3mm disc. Planning a milling cut on the rotary table will be a challenge which is what I was planning. Getting the angle between the the straight and angled section is what I was thinking about which causes you to think about how to hold.

If you want to use a rotary table then probably easiest to solder to the shaft first, you can then put a chuck on the R/T and hold the shaft. Use something like a 6mm dia cutter.

Pic of the angle for you.

Very many thanks. Really helpful and swift responses - most grateful.

I've just turned my first crank web and I'm quite pleased - now I'm at the point where I'd like to machine it into a wedge shape of sorts. The plans suggest a 3/16" 'width' at the crank end and 11/16" at opposite side if the axle hole. I marked this out on the flat by scribing the centre line on the lathe with a tool while the piece was stationary and then spacing 3/32" and 11/32" either side of the centre line - but that marking has been smudged and lost.

I'm totally comfortable with just winging it, but I'm wondering if there is a way to mark these measurements on the part 'properly'? I've just sorted myself a centre square from Chronos to put the centre line back in so I could always just measure with calipers and scribe again - but am I missing something?

To make your marking out more robust use a 60 degree pointed punch and lightly punch along the line. If it's straight then now and again, if curved closer together. If you're then filing you stop when half the mark has gone.

How did you actually mark the lines if they have been smudged and lost did you just use a marker? If you have applied marker or layout blue then scribed the line should still be there unless you did not scribe hard enough or have a very blunt scriber.

Rather than marking out the sides another option is to use various size drill bits in the two holes to set the work in the vice so it can be milled.

Edited By JasonB on 06/12/2020 07:41:48

I marked it all out, then drilled and tapped the axle hole and offset in the 4-jaw and drilled the crank hole, but then took a skim cut across the face of the web after threading it onto the axle to make sure it was parallel.

Good idea to use drillbits to hold the web at the correct angle to machine the angle - I hadn't thought about that! I guess then it is very possible to take out and re-seat the web as many times as possible, flipping it over, etc. as neccesary to get the final dimensions.

I'm using a vertical slide rather than a mill, do you have any tips on ensuring those drillbits don't vibrate out?

Take them out once the vice is tightened.