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Post by Deleted on Nov 16, 2020 16:58:22 GMT
Hi guys I need to cut an external BSP 1/4" thread to make an adaptor to fit the hydraulic pump which I bought recently for setting 4472's relief valves. While I am waiting for a suitable die to arrive from Tracy Tools (I must have every die/tap but this one)I have been looking at various charts online to ascertain what size I need to machine the bar down too. I think that I have an answer but am putting it to you guys to check. Being BSP the size of bar required to cut the thread using a die is much larger than one might ordinarily think for 1/4". The closest info that I have found to date for the external size is the thread OD which IIRC is 0.518, I'm thinking of machining the bar to approx 0.520 and going from there. My question is, does this sound right and also is there a chart out there somewhere that covers required bar sizes of external BSP threads for future jobs? Or perhaps there's a formula for such things? Over to you guys...  Pete |
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Nov 16, 2020 17:20:18 GMT
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rrmrd66
Part of the e-furniture
Posts: 339 
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Post by rrmrd66 on Nov 16, 2020 17:23:51 GMT
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Post by 92220 on Nov 16, 2020 17:43:25 GMT
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Post by Deleted on Nov 16, 2020 17:52:35 GMT
Thanks, guys.. so I just machine the bar to the thread OD of 0.518, not a fraction over as I thought prudent at say 0.520?
I guess a better question is are external threads always cut from a bar of the thread OD?
cheers
Pete
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Post by Roger on Nov 16, 2020 18:17:26 GMT
It's also in the Zeus book if you have that.
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Post by Deleted on Nov 16, 2020 19:00:54 GMT
It's also in the Zeus book if you have that. Yep, I have a few copies, what I wasn't aware of was that the thread max od was the size required, I had assumed it needed to be a fraction over. Thanks all, tomorrow I'll machine the spigot already started down to 0.518, the rest of the adaptor is ready to go...as long as Tracy Tools are as quick as normal with their delivery, tomorrow may see me ready to set the relief valves. Cheers guys Pete |
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mbrown
Elder Statesman
Posts: 1,719
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Post by mbrown on Nov 16, 2020 19:03:16 GMT
If you are using a die, there can be bit of extruison as the thread is formed, so you could probably get a full thread if you start a few thou under, rather than over, the external thread diameter.
Good luck!
Malcolm
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Post by coniston on Nov 16, 2020 21:17:44 GMT
If you are using a die, there can be bit of extruison as the thread is formed, so you could probably get a full thread if you start a few thou under, rather than over, the external thread diameter. Good luck! Malcolm Agreed, I really wouldn't go over diameter, a die is not designed to take any metal off the diameter. I think you'd end up either breaking the die, damaging the newly cut thread or at least have an unnecessarily difficult time cutting the thread. Chris D |
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Post by Deleted on Nov 16, 2020 21:29:01 GMT
Thank's Malcolm and Chris...duly noted.
Pete
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Nov 17, 2020 8:15:02 GMT
It will 'help' the die greatly if you can screw-cut a thread to around 50% depth. The die is then removing minimal material and has the cut thread to guide it.
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Nov 17, 2020 8:29:58 GMT
Ah - but you will need the famous 38 tooth change wheel for that.
I have acquired a couple of sets of Myford change wheels which I use on my Drummond, and the sets include the 38 tooth wheel. With a bit of ingenuity, it is possible to use them in set-ups to cut metric and BA threads with a high degree of precision.
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