Millers Falls power hacksaw

Hi Guys,
The piece on the saw bed that the screw/bolt goes through to tighten the vice jaws has worn nearly smooth (see photo) by mis-use over time,in fact I did not realise that there was a screw thread in there until I cleaned it up and then I could just make out the feint outline of a thread.
I am now wanting to retap the hole but what size? The internal diameter of the hole is 11/16"ths - I did have a chart that gave the thread size for different hole sizes but now when I need it I cant find it! I was thinking that a 3/4 whitworth tap would do - any ideas?
I would add that the saw is an American one and made about 1893-1900.


Any help or advice much appreciated.Thank you.
kev.

Hi Kev,

Plenty of thread charts around on t'interweb - here's a start

http://www.baconsdozen.co.uk/tools/conversion%20charts.htm

https://www.gwr-fasteners.co.uk/thread-dimensions-4-w.asp

Being American thread might have been UNC - often same diameter and pitch as BSW but different thread form. (60deg v 55 deg flat top v rounded)

Hi Paul,
Thanks for that.
You are right being American the origenal thread could well have been UNC. I will look into those sites and see what they show.
Kev.

Locknut wrote:Hi Paul,
Thanks for that.
You are right being American the origenal thread could well have been UNC. I will look into those sites and see what they show.
Kev.

Hi Kev,
I have saved quite a few as spreadsheets. If it will save time, PM me with email address and I'll send them.

Hi All,
I have at last got my Millers Falls power hacksaw up and running.
In the end I tapped the vice hole with 3/4 UNC thread and cut the corresponding thread on a bar - well pleased with the result.
I am going to power this with a Lister D and as the saw runs at 40rpm I had to make up a jack/line shaft and pulley system to reduce the Lister speed down from 700 to 40.I also had to make up a belt tensioner - crude but it works!
The metal box under the saw is to catch the swarf and cut metal - I dont want to leave metal bits on the rally field!


All the best,
Kev

Here is a photo of the unit belted up to a Lister D.The mole grips have been replaced with  a slidding bar type handle.The Lister on the right of the photo is very close to the saw,this is because at 1 of the rallies I go to space is very limited.The belt is 1",it should really be 2" but it was all I had at the time,I am hoping to find a suitable belt at the up coming rallies.
And yes it does work!

That will look good on the rally field, nice job.

Only comment to make is should the engine be on the other side so the "sag" in the belt is on the top run, not the bottom?, happy to be corrected.

Woodsman wrote: <snip> I have saved quite a few as spreadsheets. If it will save time, PM me with email address and I'll send them.

Hi Paul,

Could you e-mail a copy please, sounds like they would be handy to print off and laminate to put in the workshop.

Robotstar5 wrote:
Hi Paul, Could you e-mail a copy please, sounds like they would be handy to print off and laminate to put in the workshop.

Done.