Thread chaser

I have a fairly good set of hand chasers, but when I use them, it is all too easy for them to dig in.

What preferred method do others use?

Also, are these old fashioned, and do we buy tools with the correct thread form and radii etc ?

Bob

I'v only used a thread chaser back in the early 1960s at high school when I first cut a thread (Whitworth)on the lathe, just a light touch to form the crests of the thread form. In the early days, using a plain, non screw cutting lathe, the opperator would cut both internal, and external threads with a chaser free hand. Ian S C

If you use "lay down" thread cutting inserts you have the choice of full or partial thread form, at most you need to to round the crests with the partially cut (or use a die as a chaser)!

Edited By KWIL on 18/01/2013 11:54:39

I think Bob is using the old thread chasers that have a file handle, and a blade about 6" or 8" long, to use it you need a hand turning rest, or a bit of steel bar in the tool post, parallel to the work. Put the tool rest about the thickness of the chaser below center, lift the handle end, and lightly engage the thread, lower the handle to level . and lightly skim the thread. Thats one advantage of metric, and UNF/ UNC threads, it's only Whitworth and BA that needs the thread crests and roots rounded, and the roots are sorted by the radius on the tool tip, and a square top to the thread is no problem. Ian S C

For tidying up a screwcut thread I find a Presto rethreading file easier to use than a chaser.

Russell.

Thanks Ian. I do as you say, but just as you take your last traverse of the thread, Sod's law predicts that it will dig in and ruin the component. I wondered if the 'parallel bar' should touch the workpiece, and that the chaser should be a few thou above or below centre height. Also should the parallel bar have an angled face equal to positive or negative rake angle ?

I bought a set of chasers and handle from Tracy Tools for the ME and Brass threads. Super little set. These are ex 'Coventry dies' so have a rake angle built into them - but being realy sharp can give a really good dig in on brass/bronze.

Bob

Hi Bob

In Tubal cains "Model Engineers Handbook" the recommended back rake angle for brass and bronze is zero to minus 2 deg. Perhaps if you hold the chaser so that the built in rake is negated you'll avoid the digs in but still get the thread cleaned up as you want.

Just a thought - never used one!

Keith

I haven't used a hand chaser since I was in my teens, I think the main reasonn for my choice was that all the old turners had fingers and thumbs missing

The tool rest used for hand turning is similar to that used for turning wood. The traditional chaser is a flat bar, proberbly 1/2" to 5/8" wide x 1/4" to 5/16" thick, with a plain flat top, with the thread cut in the end, I don't know if the helix angle is included, could well be. As keith says, with brass a slight nedative top rake is needed, and zero to negative is what to use on steel as well. You could (I don't know why), make one from an old HSS tap or die, with much grinding, then silver solder onto the end of a steel bar with a file handle on it. Ian S C