Brake Screw

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Brake Screw

This topic has 6 replies, 4 voices, and was last updated 4 January 2010 at 16:11 by JasonB.

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2 January 2010 at 23:33 #46948
dolomites
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@dolomites
Where can I purchase a 16TPI square thread tap for making Allchin Brake Screw? Thanks/
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2 January 2010 at 23:33 #4903
dolomites
Participant
@dolomites
Thread Tap
3 January 2010 at 01:27 #46952
mgj
Participant
@mgj
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.
3 January 2010 at 08:08 #46958
JasonB
Moderator
@jasonb
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″
3 January 2010 at 09:10 #46960
JasonB
Moderator
@jasonb
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
4 January 2010 at 13:02 #47002
Nigel McBurney 1
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@nigelmcburney1
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.
4 January 2010 at 16:11 #47004
JasonB
Moderator
@jasonb
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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