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Chuck backplate with 1" 8tpi thread?

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Sid_Vicious:
Isn't the 60< wider than the 55< at the root of the tread?

BaronJ:

--- Quote from: edward on March 12, 2015, 12:13:49 PM ---need to check if this is an insane idea. If I were to run a whitworth tap through the UNC thread would that re-cut the 60° angle to 55°? They are both 8tpi and It should be taking material away.

Or is this mad and there is some awful disaster I am missing?  I am probably going to need atap anyway

--- End quote ---

Hi Edward,

1st I can confirm my Myford ML8 wood lathe is 1" X 12 tpi.  I checked today.  :)

As far as running a Wit tap through the UNC threads, yes it will recut the thread angle, but you will end up with a sloppy fit !

Now if you have the right Wit tap,why not get hold of a suitable piece of plate, drill it and tap it.  Make sure that you can spin it on the spindle, then turn it down to the size you want for your chuck.

edward:
I think in all honesty I will go ahead and get a tap, and have a go at making a backplate from scratch. What could possibly go wrong? :-)

BaronJ:
Hi Edward,

If you think about what you are doing and don't just jump in with both feet, you won't have a problem.  I can't remember if my Drummond lathe had a reference collar behind the threads like my current Myford ML7.  But if it does then you will need to make sure that the plate you use is thick enough to have a suitable matching mating surface machined into it.

Some one will moan, but if you can get hold of an old cast iron barbell weight, the ones that are about 1.3" inches thick and are intended for use on a 7/8th" inch bar, you have the perfect starting point.  I get things like this from my local scrapyard for pennies (OK a couple of quid) but they are ideal for this job.  I made a 5" back plate for my lathe from one. I've also made a tapping stand from a 10" diameter one.

When you come to machine one of these cast iron weights, remember to take your first cut deep enough to get under the very hard skin, even with a carbide tool, otherwise it will simply destroy the cutting edge of the tool.  Ten thou would be a good starting point.

Good luck.  Take a photo of the work and post it.  You know what they say.  :worthless:

AlanT:
You can easily run a tap through the Axminster plate and it will work fine afterwards.

A chuck plate has a "register" which does the alignment. The thread just pulls it on.

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