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Post by tomol409 on Dec 16, 2008 19:17:35 GMT
Dear AJSBSA, I have the 0 - 1/2in version of this micrometer and use it constantly when using my modelmakes lathe as it is so compact. Bought it at a car boot sale for three quid. Can't understand those who say they can't read metric micrometers. I also have a beautifully made Swiss Tesadigit micrometer which has a digital readout-worked mechanically.
Tomol409(Ariel350 NH)
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Post by tomol409 on Dec 16, 2008 19:54:07 GMT
Further to my post re 1/2in micrometer, and regarding lovely tools , I would like to mention another bargain i got at the local bootsale a few years ago. I was an L-shaped anvil with a Moore and Wright micrometer barrel mounted in the small leg. I thought- Ah - just the job for a carriage stop on the old Boxford.
However on getting it home and seeing that the barrelscale was graduated from 2.2 to 4.2 inches. ( This is a Diameter) I thought what the devil is it for. After some mental exercise I figured it out right. It was for measuring against the individual teeth of reground slitting saws to check size and concentricity.
Having one or two saws in need of a touch up, I set up my model lathe- (a Wizard lathe made about a half a mile from where I live) as a tool grinder, and ground a couple of blades up. Using the micrometer I was gratified to find them spot on.
No doubt some professional types will be familiar with this tool but I have never seen or heard of one personally. Tomol409
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44767
Statesman
Posts: 539
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Post by 44767 on Jan 9, 2009 3:08:10 GMT
I don't think this is quite correct. When cutting any thread, the tool has to be set over at the helix angle of the thread you're cutting. This is so the included angle of the thread is maintained and takes care of the side clearance issue. Take this example to its extreme where the thread has infinite lead (a spline) One can still cut this with a lathe tool set at a helix angle of 90 degrees. Of course the spindle won't be rotating and effectively it's a shaping operation.
The indexable insert tools that are used a lot these days have different anvils on which the tip sits. These come in a range of angles to allow for different helix angles to be cut- left or right hand. The angle is worked out by inverse tan of lead / (diameter x pi).
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