Trying to make sense of the threading charts

According to the chart on the front of the machine, to achieve 18 tpi I have to configure the machine like this:
1651868296067.png


a=30
b=30
Lever = 2

I don't think I have to mess with the top 40-80-40 gears - going to leave them alone. I'll start with "a" and make it 30 which will then mate to 127 idler which connects to "b" that I will set to 30 as well. According to the chart - IF I understand it correctly.

That's the initial plan anyway. Thx -
 
Bi11Hudson said:
In all of these cases, I used a 1/4 inch cutter at less than 3/16 depth of cut. The 1/4 inch tool was more than sufficient. Keep your dollars in your pocket. . .
Click to expand...
That's good to know - I'll go with what I have then, taking light cuts. I don't have to finish this thread on the stud either... I can finish it with the round die of the same TPI if necessary - I just need a proper ellipsis cut into the stud to guide the die.
 
Before you actually cut the thread, mount a dial indicator somewhere so you can check saddle movement per revolution of the chuck. If you do this accurately enough you can actually get a very precise measurement. Divide 1 by this measurement and you will know exactly how many tpi that setting has or how far out you are. Its my way of double checking a new / unknown machine.
 
fitterman1 said:
Before you actually cut the thread, mount a dial indicator somewhere so you can check saddle movement per revolution of the chuck. If you do this accurately enough you can actually get a very precise measurement. Divide 1 by this measurement and you will know exactly how many tpi that setting has or how far out you are. Its my way of double checking a new / unknown machine.
Click to expand...
OK. That's after I do the transmission 'surgery'...
 
"surgery" will only take you 5-10mins once you get the hang of it.
Make sure you have some clearance between the gears when positioning them so they don't run noisy and there are no high spots. I work from the bottom up when I do this.
Then i set the qcgb and check the pitch after that. Go for the lowest speed you can choose, and go for it.
 
"General Practice" is often a misleading term to a novice. I refer to the following as general practice simply for lack of a better word.

(1) When setting the "banjo", the manual recommends passing a piece of paper between the gears to set spacing, hence backlash. I use currency paper, a dollar bill, simply for consistancy, the note paper I keep handy varies quite a bit in weight.

(2) There is a technique used even by experienced machinists called a "scratch pass". The cutter is set so slight as to scratch the surface of the work, then checking with a thread gauge. Even well experienced people use this technique "just to be sure" as one little mistake or forgotten step in the setup will bite your a$$. It WILL bite, usually when you least expect it.

(3) The threading chart shows the 127 tooth gear in the setup. It can as easily be the 120 tooth, a 100 tooth, or any other. It is simply an idler gear and has no purpose other than as a spacer. It only matters in spacing the banjo.

.
 
After a weekend of graduation parties and mothers day events I'm back to the lathe project:

This morning before work I took apart the lead screw gear and the stud gear. Turns out I didn't even have to mess with the two stud gears because they were already what I need for Standard threading anyway. Still, I didn't know that at the time and began unscrewing the stud/shaft partially - that's when I noticed that the stud/shaft is BENT - and it was not going back in there straight at all - that shaft and gears on it had a very noticeable wobble. So I took it out all the way to inspect it... sure enough: it's bent, and also noticeably worn - I can't use it in this way.

Not sure how well it will show in pictures (the one on the right shows it more clearly). It's not that noticeable until you start screwing it in.

Another day, another setback.... will have to order a new one.
 

Attachments

  • bent_stud1.jpg
    bent_stud1.jpg
    164 KB · Views: 84
  • bent_stud_2.jpg
    bent_stud_2.jpg
    38 KB · Views: 87
Last edited:
I ordered the wrong part... Feels like I'm digging a deeper hole. I'll try to straighten out the bent shaft and see if I can do it right - it doesn't need that much. Measuring the thread major it reads .302'' and 20tpi. Does that translate to 5/16'' 20tpi? I'm thinking I'll drill a hole in a scrap piece of metal and tap it to that size so I have some leverage to straighten out that shaft.

The yak shaving continues...
 
Last edited:
Asian lathe? Likely to be M8. The pitch on M8 is 1.25mm which is equivalent to 20.32 TPI. Minimum major diameter is 7.760mm = 0.3055" which is quite close to what you measured.

5/16" min major diameter is 0.3026". But 5/16" common sizes are 18 TPI and 24 TPI, don't believe there is a 5/16-20 screw that is commonly available.

My guess, it is M8-1.25.
 
You must log in or register to reply here.
Back
Top