Ratchet wheel

[Pete RimmerParticipant @peterimmer30576]

I would turn a centre to fit in the dividing head taper. I presume it's a morse taper 2 or 3? Turn it from 1" mild steel and then turn an arbor for your ratchet blank on the opposite end, with a thread for a retaining nut. and centre-drill the ends.

Mount your taper in the dividing head, load the blank onto it securing with the nut, hold the outboard end with the tailstock centre and now you can cut your ratchet with an end-mill to however many divisions you might want.

[BazyleParticipant @bazyle]

I suggest drawing it several times scale and maybe cutting it out of cardboard to get a feel for the shapes. Unlike a gear wheel you do not have to get things so precise and the teeth can be cut to a depth that 'looks right'.

Start with the diameter and work out the circumference. 1.5 x 3.14 = 3&3/4.
Think of a suitable size for the teeth that looks right, say 1/6 in. Divide that into your circumference. 3.75/(1/6) = 28.
Heck 28 is near enough 30.

I now suggest using a dovetail cutter with a 60degree slope to cut the teeth.
Cut out a cardboard dovetail cutter to place over your drawing of the wheel. The cutter axis will be coming down vertically so keeping it vertical move it round the edge of the wheel until it sloping bit of the cutter edge is along a radial line from the centre of the wheel. This is no good because you need an 'undercut' to trap the pawl. Move it further until you get some undercut, about 10 degrees.
Allowing for the scale of your model measure the distances between the vertical centre of the wheel and the vertical line of the cutter and the bottom of the cutter so you can duplicate it on the mill.

You will have to move the cutter in sideways because of the undercut required. Set up a depth (sideways) stop.
Cut the first tooth (well gap actually) quite shallow. Move the blank round and cut the second to the same depth. The 'point' of the tooth formed should still have a flat on it uncut. Increase the depth of the cut until this flat is small but not sharp.

[Matt AndrewsParticipant @mattandrews73332]

Thank you for the responses. I have a better mental image now. I need to try a fly cutter to see if it works. I have a dumb question still.

When the fly cutter tool bit enters the cut is it the flat side of the bit that leads into the cut or is it a shearing cut from the inside and finishes the cut with the tooth form.

I cannot find a ” how to online”

Thanks
Matt

[Martin ConnellyParticipant @martinconnelly55370]

Sound a bit like you are asking about climb and conventional milling. Look this up and it should apply to your question. Let us know if this is the case. I think there is something on this on the model engineer web pages.

Martin C

[Matt AndrewsParticipant @mattandrews73332]

Thanks for the reply. No I am not asking about climb vs. Conventional milling but about the flat face of a single tooth form tool (fly cutter) coming through the cut. When I try to visualize the cutting action it seems that it is just a flat face with relief behind that flat face pounding on the work and it doesnt make sense to me. I feel like the form of the tool should be maintained but that there should relief on the front face of the tool bit so that from the moment of impact there is a shearing action through every phase of the cut.
This keeps me up at night I hope that someone can help me get some sleep.

Thanks and Best
Matt

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Matt Andrews on 05/10/2018 03:21:24:

 

….When I try to visualize the cutting action it seems that it is just a flat face with relief behind that flat face pounding on the work and it doesnt make sense to me. I feel like the form of the tool should be maintained but that there should relief on the front face of the tool bit so that from the moment of impact there is a shearing action through every phase of the cut.
This keeps me up at night I hope that someone can help me get some sleep.

.

I think I see what you are visuallising, Matt … and I'm pleased to say that NO it doesn't really happen like that.

Your visual model needs to include 'speeds & feeds'

With the cutter whizzing round rapidly, and a comparatively slow feed; the cut is an arc, and starts very gently.

Draw pictures, or make big models, but don't lose sleep … it's all fine.

MichaelG.

.

P.S. suitable grades of brass cut perfectly well with zero rake on the tool.

Edited By Michael Gilligan on 05/10/2018 07:02:30

[Author]

Posts