Which tap for project

Hi

I am in the process of making a fly tying vice, the design of the jaws is a little like a small toolmakers clamp, twin screws with opposing forces. My design will use left and right hand pitch threads for the front screw with the adjuster wheel mounted between the jaw plates pulling the two jaw plates together to lightly clamp the hook in place. I will be incorporating a cam at the rear screw location to give a fast acting tension cam forcing the rear of the jaw plates apart.

My question is should I use 24 tpi, 32 tpi (M5 metric) or 36 tpi (M4 metric) for the front fine tension screw?

The jaw plates will be approximately 12mm high and about 1/4" thick near the front tension screw location, possibly slightly thinner once fully machined.

Ideally there should be a little slop in the threads to allow a little movement in the front tension screw assembly to allow the tip of the jaws to move sufficiently to lightly hold the hook before binding up.

I was going to try 10 X 24 OR 12 X 24 UNC for the front screw or M5 x 0.8 or M4 x 0.7?

Any ideas on the best option?before \I order expensive taps from the USA?

The jaws will be made from 01 carbon steel (ground flat stock) or D2.

Thanks in advance for any advice.

Kevin.

I can't comment on your thread choices but wondered why you would order expensive taps from the US when tracy tools do quite economic ones in those UNC & metric sizes..unless you're planning on making dozens of these tie clamps...?

Hi

Thanks for the reply, I have a friend in the USA who is scheduled to be in the UK for a few days in a few weeks and I can order the taps and dies from a USA supplier (if UNC is my best option) as they are made in the USA and HSS, I have good quality HSS right hand UNC sourced in the UK but UK made left hand taps and especially dies in HSS are fairly expensive. The same specification made in the USA can be sourced much cheaper except for the postage. With the postage being FOC if a friend brings them over I should be onto a winner but it will still be about £50.00 for only a few taps and two dies all in left hand hence my question on most suitable pitch.

I have used Tracy Tools several times and had great service I just thought HSS would be better for 01 or D2 steel if I end up making a few sets of jaws. With the cost increasing by a factor of 4 for this specification from Tracy Tools I am cheaper sourcing the tooling in the USA if 24 tpi is deemed to be better for this application.

Kevin

I suggest you pick a tap size you are likely to use for future projects, otherwise there is not much to recommend one over the other.

Just as a 'Curved ball' and not for this project, but if one needed small left and right opposed threads with an adjusting wheel, you could cannibalise a set of springbow compasses ?
BobH