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| minerva:
As a “returnee” to our all absorbing hobby I have reached that point on the learning curve whereby many of the long forgotten skills are returning to haunt me. The mysteries of heat treatment and single point screw-cutting to order to mention but two . I currently have two projects on the go, viz. - the manufacture of a George Thomas's Versatile Dividing Head (VDH) and a worm wheel controlled Rotary Table. Both projects sourced from Hemingway Kits here in the UK. Both projects have one thing in common the cutting of bespoke threads. The main spindle assembly of the VDH for example requires the cutting of three different sized BSF threads namely: 1. 1/16'' x24 TPI 1''x 24TPI and finally 5/8'' x 24 TPI. Coupled with the fact that I have recently upgraded my mini lathe to a 9x20 which came fitted with an integral thread cutting gearbox I felt some practice was called for before I committed valuable project component material. I read and re-read Martin Cleeve's excellent book “Screw cutting in the lathe” (number 3 in the workshop practice series) and managed to divine sufficient information about the various thread diameters to contemplate an attempt at the various threads involved. I possessed no dedicated thread cutting tooling and decided after seeing this post :proj: :proj:http://madmodder.net/index.php/topic,3523.25.htm to have a go at making my own, the machining was fairly straightforward and went quite well but come the time for heat treatment I was forced to look up the procedure and was most surprised when the simple procedure of both hardening and tempering of the Silver steel blank went without a hitch and after touching up with a diamond slip stone I was ready to go. At this juncture I will confess to an almighty 'C**K-UP – I, through lack of concentration bored the main casting of the VDH some 20thou. Oversize which has meant a rethink on the sizing of the spindle dimensions which is no big deal as the threads involved can remain as per the origional design ( I hope) the solution requiring only a replacement spindle blank. The dilemma now was quite straightforward do I turn the male threads first and make the nuts to fit or vice-versa ? My strategy was quite simply to try initially each option in turn in order to ascertain the most successful. Now the results whilst satisfactory raised more questions than answers. Making the nuts first proved to be the quickest of the options altho' the fit was somewhat loose giving doubts as to the accuracy of the minor bore dia. Divined from the formula in Martin Cleeves book. Machining the male thread first followed by the nut took much longer to achieve but a much better fit was achieved. My question is quite simply. What do you old hands do? Have you a rule of thumb to determine the various bores, dias etc. and what factors determine whether the male or female threads are cut first. Hoping this rather wordy post won't bore too much Kindest regards TerryT AKA minerva Edit : link fixed ,Rob |
| Lew_Merrick_PE:
Terry, As a general rule (i.e. subject to exceptions) you will want to turn the female thread first and use it to gauge the male thread. The theory here is that you can just move all your set-up aft to place the (generally shorter) female thread over the male thread rather than move things off-lateral position to fit the male thread into the female thread. Does this make sense to you? |
| BillTodd:
Hmm, interesting I usually make the male first - it's easier to measure (just wires & a mic) Bill --- Quote from: Lew_Merrick_PE on January 01, 2013, 07:45:03 AM ---Terry, As a general rule (i.e. subject to exceptions) you will want to turn the female thread first and use it to gauge the male thread. The theory here is that you can just move all your set-up aft to place the (generally shorter) female thread over the male thread rather than move things off-lateral position to fit the male thread into the female thread. Does this make sense to you? --- End quote --- |
| minerva:
well Lew / Bill as I suspected there may not be any laid down answer to this question but from a novice position there must be an acknowledged"way to go" in order to put oneself in the ballpark of a reasonable result. Bill, I have read of the wires and Mic method but never tried it perhaps now is a good time to try it, I am going over to ARCtrade euro tomorrow so I will suss out the relevant kit Lew I take on board what you say and it makes sense. You make no mention of the bore sizes used.Do you divine these from data books/tables or rule of thumb ? |
| ieezitin:
Assuming you are turnng between centers or using the tailstock with a live center i would make the male thread first and get the piece close who cares if its under a little, if you take it out to test on the female its a little tricky to put back while engaging it back with the lead screw. All to do then is to make the Nut and keep testing it to the male piece. If you're not using the tailstock it dos'e not matter. keep on testing brother and have a test fest. Anthony. |
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