Who needs metric threading gears?

[martik777]

I needed to make a short (3/8") metric thread of unknown size (2.45mm OD), closest I could match was a bit smaller than M3 .5mm, so I figured it must be a M2.5 .45mm.

Closest thread on the QCGB was 56 tpi (1/56=.0179; .45mm = .0177) and it worked perfectly. I even forgot to set the compound to 30degrees or set the threading bit perpendicular and it still worked ok.

I don't know how well they would match up with coarser threads but this saved me buying a special die.

 

[4GSR]

Yep, Did it one time, cut a 1.5mm using 19 t.p.i. setting on my 9" SBL. The thread was only .1/2" long, lead error was only .0032". Used it on a ER32 collet nut.

 

[martik777]

The equivalent in imperial is 16.93333 so I assume you meant 17tpi? 19 gives you .05263; 17 gives .0588 1.5mm is .0591 How did you get that setting on the SB 9 gear box? I wanted to make a chuck to fit one of those ER nuts but couldn't come close enough without changing the stud gear or using transposing gears. Threading via a feed rate of .0594 (position A5) and NOT using 1/2 nuts comes the closest to 1.5mm

 

[4GSR]

I may have missed the pitch by a number or two, this been over ten years ago.

I have a 9" SBL that started out as a Model C workshop lathe with loose change gears. Over the years, dad and I upgraded it with a QC gear box bought from a old New York Jew as well as a apron and wore out cross feed screw with the integral gear.

Anyways, what I did was used some of the "loose gears" from the model C gear stack to come up with the odd pitch using the QCGB. All you have to do is change the ratio between the stud gear and gear box input by four teeth and you change the pitch by 1 thread per inch.

Ken

 

[benmychree]

I needed to make a short (3/8") metric thread of unknown size (2.45mm OD), closest I could match was a bit smaller than M3 .5mm, so I figured it must be a M2.5 .45mm.

Closest thread on the QCGB was 56 tpi (1/56=.0179; .45mm = .0177) and it worked perfectly. I even forgot to set the compound to 30degrees or set the threading bit perpendicular and it still worked ok.

I don't know how well they would match up with coarser threads but this saved me buying a special die.

There are a few thread pitches where English and metric pitches are close, but only if the length of engagement is relatively short due to the accumulated error on lead; if you are just screwing a short nut on, it may be accurate enough if the thread fit is not important and the thread may be cut a little undersize to make up for the lead error. I think the metric lead 1.5 is one that is fairly close to an (nearly) equivalent English pitch.