15423RE: [MedievalSawdust] Re: Vice screws ?
- Nov 17, 2012
The chart for your percentage is all about thread engagement amount, not a looser or tighter fit. The fit is based on the diameter you cut. That is why good die sets are adjustable, for example. You loosen or tighten the diameter of the die slightly, to compensate for the difference in what you need and what the die is currently cutting with the specific material you are using.
Did you really mean you were cutting .0005 at a time on a lathe or did you mean .005? The basic idea is still the same for a custom fit. Get it close with your mics, check it with the nut, cut a few more thousands off, deburr, check again, etc.
So much for metal screws and threads.
On to wood threads.
To answer the previous question about the screw box cutting threads too close in size to the tapped nut. Assuming you are making the Roy Underhill style of box, you need to add a jack screw to his design. Put it so it touches the back of the cutter and will push the cutter forward toward the tapped hole. You will use this adjustment to move the cutter in or out to cut a small amount more or less off the threads on the rod. This is how you get the threaded rod to properly fit your nut. Once again it is a, cut it, deburr, check the fit, cut again, etc.
On the larger threads, you may be taking too big a “bite” using only one cutter, making it too hard to turn, breaking the dowel, etc. If so, you need to install a second cutter on the opposite side of the box. It should be as close to exactly the same as the first one as possible. You also will have to adjust the depth of the slot it rests in as the thread on the opposite side will be deeper.
Edward of Freeholt
Vert, a double-bitted axe and on a chief embattled Or an arrow sable
From: email@example.com [mailto: firstname.lastname@example.org ] On Behalf Of d6crawler
Sent: Saturday, November 17, 2012 11:46 AM
Subject: Re: [MedievalSawdust] Re: Vice screws ?
Metal screw threads are also cut based on a target fitment. If you need a tight fit for a particular application then you consult a chart that tells you how big of a hole to drill or how large of a rod to use for an 85% fit, etc.
When cutting threads by hand on a lathe you keep the nut handy to know when you have gotten it to the fit you would like. Once you are close you cut a bit, check, cut another .0005, check, ...
From: K <kaisaerpren@...>
Sent: Saturday, November 17, 2012 8:20 AM
Subject: [MedievalSawdust] Re: Vice screws ?
I have done this. I also have 2 smaller comercially made screw boxes.
I found/find that I have a problem with the finished screws. when you make a screw box with the tap that you will use to make that nuts, the screw is to tight in the nut. Metal bolts and nuts are not Exactly the same size. the nut is made a tiny bit big and the bolt is made a tiny bit smaller. otherwise the friction would be too great and ruin the assembly.
I have solved this by carving the larger screws. and chasing the smaller ones.
or another solution would be to make certain that the nut is bone dry when you make it and the screw is slightly green when you make it.
Oh and when you calculate pitch and screw size, Always go from the greater diameter. it just works easier.
also change the angle between threads to 90 degrees for larger threads.
historically, very few screwboxes seem to have been made. they do show up occasionally, Heron (also called Hero)illustrated one over 2000 years ago. however most of the evidence I've seen seems to indicate that most screws were made by "chasing" or carving methods.
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