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Brake Screw

Thread Tap

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dolomites02/01/2010 23:33:54
1 forum posts
 Where can I purchase a 16TPI square thread tap for making Allchin Brake Screw?  Thanks/
mgj03/01/2010 01:27:01
1017 forum posts
14 photos
No Idea.
 
Try grinding a tool up and cutting the thread . Or you you can cut the tthread as an external thread in silver steel and make a tap.
 
I have  the same problem coming, and the latter seems the best idea because it involves only one set up.
 
OTOH, I might do it the other way because its more interesting, and not difficult.
JasonB03/01/2010 08:08:58
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25215 forum posts
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I've just made the 1/4" x 16 brake rod & nut for my 2" Fowler.
 
When you are set up for cutting the screw make another out of silver steel which can then be made into a tap.
 
I tried cutting the nut butas the bore is only 3/16 I found that when screwcutting it the tool flexed too much so I used the lathe to cut most of the thread and then resorted to the tap to chase the final finished thread. I'll take a pic of the tap later.
 
Jason
 
PS I'm assuming you are doing a 1 1/2" alchin and not a 3" in which case you could probably get away with an Acme thread which Tracy Tools sell down to about 3/8"
JasonB03/01/2010 09:10:25
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Here is the pic, if I were making it again I would go with a longer tap to get a more gradual taper but it did the job.
 
The brake rod is all one piece, the small amount of silver solder is where I soldered in two half rounds of steel to fill the tool run out groove as the original had no groove.
 
The nut was cut from bronze and the silversoldered into the fork.
 
Just had a look at the Alching book and as the thread is only 5/32 I think you will have to go straight in with a tap, Hughes gives a good description of how to make a suitable tap in his book.
 

Jason
Nigel McBurney 104/01/2010 13:02:13
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1101 forum posts
3 photos
Hi I made my Allchin brake screw about 40 years ago,all the above is good advice,but they have forgotten clearance on top of the thread,make the tap about 6 thou larger on the outside diameter and also cut the thread depth a few thou deeper on the tap,a little side clearance is also required on the thread,about a thou or two or it will bind in the nut. A long tap with a slow taper is good advice. In recent years I made a screw and nut for a full size seven ton Aveling and it was probably easier as both thread and nut can be screwcut.On some old machine tools and the screws on old antique dining table the thread was machined and the nut was cast around the thread using white metal.
On normal square threads clearance between the top of the screw thread and  the thread in the nut was a standard ten thou irrespective of screw dia. 
JasonB04/01/2010 16:11:01
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Hughes gives all the relevant clearances in his description for making the tap, the Fowler build manual I am using does the same.
 
Jason

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