Hello Ray

Your metric Harrison 155 should be the same as my Harrison 140, which came as metric only.

The standard metric gear set is 25-100-80 (top-intermediate-bottom).

I think, that if you put a gear set of 50-63/40-120 on (which I have) then the metric gearbox will give the full set of imperial gear pitches, with the layout looking very similar to the imperial gearbox. I managed to buy the extra gears by asking around the dealers for a month. I don't think you will find a 127 for the Harrison, and I recall that it might not fit the quadrant anyway.

There is more on this and some tables on the Harrison Yahoo site, but it is not easy to find past threads. If you message me with your email I will send you a copy of the table that I made.

Norm

If your lathe is supposed to use a 120/127 combination for the metric-imperial transposer then you can susbtitute this for 34/36 and the result is very close indeed – less than half a thou over an inch of thread.

So for a 6mm pitch screw:

6*36/34=6.35294 x4 /25.4= 1.00046"

You'd be hard-pressed to cut a thread that accurate.

The extension gear sets for dividing heads often contain 34 and 36 tooth gears. Come up on that action site a time or five a year, usually sell cheap because folk don't recognise what they are. Once separated from their mating dividing head its nigh on impossible to figure out which one they actually fit.

HPC list 34 and 36 tooth gears in most sizes. Larger ones aren't exactly inexpensive tho'. Sometimes its best to bite the bullet and just buy something retail rather than wait ages for a bargain. Its what I did to fill out the set for my Smart & Brown 1024. Still be looking otherwise!

Clive.

Hello Ray,

I've just stumbled across your post and the problem you have.

Pete Rimmer is quite right with a working alternative of 34/36 for the translation gears of 120/127, it is based on a ratio module of 17/18.

I don't know what gears you are equipped with but by multiplying the basic ratio (17/18) both top and bottom by 5, you finish up with a combination of 85/90 which should nicely fill the gap to link your top shaft and bottom shaft. The threading error that gives you is still negligible.

If you still have a meshing problem with those sizes try 35 and 70 for top shaft and gearbox drive instead [if you have those] or an idler in the chain if not.

I hope that helps you

Regards Brian

Just to let you know that I can 3d print, highly accurately and in high impact materials any change gear you may require. Pm me for details.