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MG Midget and Sprite Technical - DIY swivel pin reamer

Finally got pics to computer.

I was very much in a hurry when I made this, and meant to make another if it worked. But, it works so well that I haven't done so.
Pics are about that crude too, sorry. Main point is that only about .030 at the end, on two faces, actually matters. While the actual cutting corners should be in line such that they share the load, it is not necessary or even desirable that all the spacings and angles be exactly equal. On the/at basis, I measured nothing - all freehand & eye.

FRM

FR Millmore

#2

FR Millmore

Final

FR Millmore

FRM,

Good you posted the last photo for others as I was just about to say a close up would be nice to clarify the details for others. I knew what you meant as I've used a similar procedure to make sets of valve seat cutters.
David Billington

David-
Always hard to figure out how much instruction is required.
And really hard to see what the pics look like in the camera previews.
Note that if the pun you use is actually worn undersize a bit, the new one might be tight.
In that case I finish with a brake hone.
But generally, the lower bearing surface is pitted but not really undersize.
It is also commonly not necessary to renew the top bush. Check the play with the new pin first.

FRM
FR Millmore

FRM, that's brilliant. Ta very much. No doubt we'll all get busy with grinders now. :)

As regards how much detail you should in the instructions, I don't think you can include too much. Dunces like me need it all :). Seriously though, it helps to answers the questions before they get asked.
Lawrence Slater

So, to make this you:
1. Make 3 (or more?) cuts into the shoulder of the pin at 3 degrees to the axis of the pin. Looks like you used a thin angle grinder disk. Is that right? These are to act as flutes to clear any cut debris.
2. Create a cutting edge on the intervening spurs of metal left between the first ground flutes, and with a "back angle" behind the cutting edge. I presume these are done with a fine file and then dressed (sharpened) with a stone? Looks a bit like a chain saw tooth to me.

Is that about it? Do you then use a lubricant when using it to ream the bushes?
Guy Weller

Lawrence-
More info is good, but I've been studying this stuff all my life, in great detail, and could not write all of it in the rest of my life!
Plus it gets intimidating, and I believe people should try stuff and think about it. If you just follow instructions, you are screwt if something is out of the instruction range, but if you think, you might solve your problem and discover something new. And it is surprisingly difficult to predict what people perceive despite what you think you wrote.

Guy-
1) Actually there are about 8 flutes. Not really necessary but when you screw up the angles on a tooth or two, you still have enough good ones!

2) Yes, angle grinder for the flutes, and the end relief. Leaving about 1/16" of the original machined angled shoulder as a reference. Then grind the cutting face of the flute with a fine wheel in a Dremel, to be more or less radial and at the more or less 3 degrees. Use a cutoff wheel on the Dremel and go straight in as a plunge cut; you can see this in the pics, it maintains the clean edge. Then fine grind the end clearance similarly, maintaining the shoulder angle and again about 3 degrees end relief, until you just eliminate the reference part from the rough grind. The pins are fairly hard, and if you grind such that you do not overheat the metal, they stay hard.
Deburr OD edges with a fine stone if necessary, but DO NOT destroy the sharp bit!

Irregular spacings and slight angle variations prevent the reamer from chattering or jamming.

Any oil will do, but thin stuff washes the flutes clean as you go. Grease is good when you want to catch the swarf, but you need to clean them out, not here but sometimes.

Add for LS:
It actually took me as long to write this clarification as it did to make the reamer!

FRM
FR Millmore

Thanks Fletcher, for the added detail.

Incidentally, your comment to Lawrence pretty accurately describes how he usually goes about things anyway!

Guy
Guy Weller

Yup thanks for that Fletcher, and I agree with what you wrote about instructions too.

True Guy, that does just about sum me up. :)
Lawrence Slater

This thread was discussed between 16/06/2012 and 17/06/2012

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