Graziano change gears

Hi all!
I’ve been restoring a Sag 12 for the past few months and it’s finally up and running! I ran a few projects though it last week and it did really well. However I would like a slower setting for the feed box. I have the 20 51 80 change gears but am missing the 31 58 47 64 gears for the Mod and Diam Pitch settings. Not sure if this would make a difference but it would be nice to have some more gears to play with. Any Sag 12 owners out there that care to weigh in or have any advice? Thanks! -Cody in Seattle

Here are a few photos:View attachment 228056

You can always find out what you have in the way of Module and make or have made gears with any number of teeth you want

Say on the 51 - if it was 106 OD then the module would be 2

A 2 module 51 tooth gear will have a pitch diameter of 102 and an OD of 106 - because the addendum is 2mm

You can work this backwards - you check the OD and find it to be 106. You count the 51 teeth and add two to that count.

106 divided by 53 is 2

Cody,
Good to hear your lathe is running.

You can get the full range of feeds with the gears you have. I have never used anything but the 20-51-80 gears.

BTW, if you put on the other gear combination (31-58, 47-64), your feed range will go faster, not slower.

With the gearing you have, you can get 60 feed rates from .0023" to .025" (i.e. longitudinal feed in inches per rev of the spindle)

If your lathe is an "inch" version (i.e. dials are in inches), then your feed chart should also be in inches:

Slowest feed: .0023", use W B 10 (select using the two levers and one dial).
Fastest feed: .025", use M A 10.

If you have a machine with metric dials, the same lever and dial positions are used, but the chart will read 0.06 (slowest) or 0.64 (fastest), these being mm per rev of the spindle.

Let me know if this is not clear or if I am on the wrong track.

Additional: if you are turning and decide you want to change the feed rate slightly up or down, just rotating the 1-10 dial will give good results. Rotating the dial can be done with the machine running, well I do anyway.

For example, if you have the levers set to M & C, then rotating the dial 1-10 will give you a feed range from .0063" - .0125" in approximately 1 thou (.001") increments.

Likewise, with levers at M & A, rotating the dial 1-10 will give you a range from .012" - .025" in increments.

It is a well-thought out gearbox.

Cody,
I see you have a pressure gauge on your transmission oil pump - could you please tell me what pressure you have?
Thanks,
Peter

Thanks so much for the reply’s.

Johnoder: Awesome gear info! I was considering making some new gears, but now I don’t think they are the problem. I ran the stock sizes I’m missing through Geargenerator.com and came to the conclusion that they would run faster. Peter also confirmed this.

Peter: Thanks for the tips and great detailed explanation. Moving the 1-10 dial while the machine is running works really well. So to take a few steps back I am having trouble getting a smooth longitudinal cut on 6061 aluminum without any threading marks using the WB10 setting. The cross feed finish looked like a mirror but the feed I was using was much much slower. I think I will try again using some different spindle speeds, or maybe I’m overlooking something completely different.

Oil pressure: Cold start I get about 80 psi. After a few minutes the oil warms up and it drops down to 40-35psi.

Cody,
Thanks for the oil pressure info.

Regarding finish on your longitudinal cuts, I am guessing it is a tooling problem. What are you using?

BTW, I didn't realise until now that the cross feed rate is half that of the longitudinal feed rate, I haven't checked it myself but that is according to the manual.

Peter, that makes more sense that it’s a tooling issue. I’m using a ac820p coated carbide insert. I use a lot of different materials so the local tool shop set me up with this as my “general purpose” insert.

You can buy gears that you have to turn the hole to size real cheap
I pay €45 for a M1.5 z=127
peter

Cody,

I think it would pay to start a new thread asking specifically about how to get a good finish. Give as much info as possible - material type, diameter and speed and feeds you have tried, also more detail about the insert.
Peter

Thanks Peter that’s a good idea. I will do some more experiments and research this weekend and follow up with a new thread.