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Screw cutting in the wood lathe

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Wildman

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having seen a number of screw cutting devices offered and now having a real grasp of how they work but put off by the price I have decided to make my own. The device itself is straight forward enough and making the cutter straightforward once I establish a few things.
I am assuming the following
1) TPI the same as the spindle nose thread makes it possible to make screw on wood chucks.
2) the total length of thread that would need to be turned probably no more than length of the spindle nose.

The diameters required to be turned are from max lathe capacity to the smallest likely to be used, The dia of the cutter must be smaller than the smallest dia thread to be cut so how small would the experienced turners suggest for a start. After all I can always make a smaller cutter later if required, what is the dia of and how many teeth are there on the proprietry item that you have.

what drawbacks have you found, what changes/ improvements would you like to see.
 

dickm

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Not exactly a reply to your query, but have you thought of using a standard steel tap? If you have a Record/Coronet/lots of other lathes with a 3/4" by 16 tpi nose, that's 3/4 UNF and readily available. Some of the other lathe threads are also recognised standards, although not as common as UNF.
 

Wildman

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to answer the above, thread chasers only work well if you can run slow enough or hitting the bottom of a blind hole will just churn the thread out. So This will use a spinning cutter onto which the work is fed. My coronet is 7/8 x 16 TPI and I do have a tap/dies etc. and indeed could screwcut on my metal lathe but fancy the challange. Thinking of pot/jar lids, walking canes, etc. Feeding long objects is one of the design problems to be overcome once a chuck fed devise has been built. however I see no problem with long items the idea is already in my head.
 

boysie39

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I think it was George Watkins (Cornacopia) who posted a nut and bolt he had turned on here .I think maybe CHJ may have posted something similar if memory
serves me right, I could be wrong of course . It is a couple of years ago . It may help you .
 

tekno.mage

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Take a look at my post:

prototype-thread-cutting-jig-t43205.html?hilit=%20thread%20cutting

Which details a thread cutting jig my partner & I built a couple of years ago and are still using today. We used a 3/4" 16tpi threaded rod as the leadscrew and a 60 degree double angle cutter to cut the threads. We have since also built a 1" x 8tpi version which uses a home made cutter.
 

Wildman

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my last post seems to have disappeared, cheers Kym, that is the same design as mine apart from the x-y table.
As my saddle locates on a round bar I only have to slide the work up to touch the cutter and lock it off. Then release the saddle location and raise it to feed the work into the cutter path by the thread depth. which for 16 tpi is .0812" so 81 thou measurements in imperial rather than mix metric and imperial.Thread depth taken from the Engineers bible "Machinery handbook". I will be looking at a cutter of around 1/2" in dia with a max thread length of 1" should be enough to cover all manner of things. If I get a chance I'll also try the slitting saw idea for square threads, I have a selection to hand but suspect the threads will break off.
Just had another though and will try using a countersink drill for a sawtooth thread form, readily available.
 

Wildman

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cheers Jon, I have seen those and don't feel like spending the money when I can make one and enjoy the making.
 

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