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View Full Version : Lathe Feed Chart Vs Threading Chart



adamsgt
12-15-2016, 01:10 AM
I was going over some charts for my lathe and got confused over the meaning of the Feed Chart versus the Threading Chart

http:// (http://<a href=&quot;http://s248.photobucket.com/user/adamsgt/media/lathe%20gears/DSCN0661.jpg.html&quot; target=&quot;_blank&quot;>http://i248.photobucket.com/albums/gg182/adamsgt/lathe%20gears/DSCN0661.jpg</a>)http://i248.photobucket.com/albums/gg182/adamsgt/lathe%20gears/DSCN0661.jpg (http://s248.photobucket.com/user/adamsgt/media/lathe%20gears/DSCN0661.jpg.html)

My lathe is set to the gear configuration N shown in the threading chart. Going between configuration M or N requires the swapping of gears 21 and 42. So that means that there are only two configuration for the X and Y as shown in the feed chart. That is 42 and 21. However the feed chart does not show any feed rate that is a combination of 21 and 42. So it appears to me that the feed chart is useless to me. Am I missing something fundamental?

Rflshootr
12-15-2016, 02:06 AM
If I'm understanding you correctly......look at the feed chart on the machine. The note at the top says "42 & 21" are mounted initially and should correspond to the chart on the machine.

TRA
12-15-2016, 03:27 AM
If your machine has a gearbox driven by a round shaft with two keyways,,,,,the 42/21,..... just sets the box up for fine or coarse feed.

Same as the lead screw gearbox, one way sets up the fine threads, and switching the 21/42 sets up the coarse threading. The rest of the gear changes are done in the quick change box.

Jerry H
12-15-2016, 05:23 AM
The feed rate chart is for turning and the thread pitch chart is for when you are threading. You will likely do most of your turning with the 21T on X and 60T or 30T on Y. You will likely do most of your threading with 21T on X and 42T on Y. Note also the top gear combo is 24T & 72T for feed and 32T & 64T for thread.

adamsgt
12-15-2016, 01:13 PM
The feed rate chart is for turning and the thread pitch chart is for when you are threading. You will likely do most of your turning with the 21T on X and 60T or 30T on Y. You will likely do most of your threading with 21T on X and 42T on Y. Note also the top gear combo is 24T & 72T for feed and 32T & 64T for thread.

So what I'm getting from this is that I'll have to change three gears when I switch from turning to threading and back. Ouch, makes a lot of extra work when I'll be turning and threading a tenon. Or, leave the gears set for threading and take whatever feed I get for turning.

This is a used lathe that I bought some years ago from a dealer who bought three of these from a shop. Two seemed to be in decent shape and this one of the two had the lathe bed already sealed up with a discharge port for liquid. So It's ready for a flush system. The skimpy manual had two pages of feed and threading charts. One for a metric leadscrew and one for an imperial leadscrew. The page for the metric leadscrew says that it comes with 13 change gears while the imperial leadscrew comes with 7 change gears. What is the best or easiest way to determine which leadscrew is on this machine? I think the one I got came with more than 7 gears but less than 13. As soon as I post this I'm going to my shop to check those gears one more time to see what I've got. I do remember that when I first attempted to thread I wasn't getting the thread pitch I set so I checked the threading chart and set the gears into configuration N and that worked. That's about as far as I've gone messing with the gears.

Jerry H
12-15-2016, 01:48 PM
Check the pitch of the lead screw to determine which it is. It should be exactly 8 TPI for imperial though I have heard of 16 TPI lead screws as well. Do you have a brand name and model number tag?

jackie schmidt
12-15-2016, 04:35 PM
As Jerry said, just use a steel rule and count the threads.

If it was originally sold in the US, it probably has an imperial lead screw.

Keep in mind, if it has a imperial lead screw, you cannot dis-engage the half nut when threading metric, and visa-versa.

CMaier
12-15-2016, 04:43 PM
NO YOU DO NO NEED TO "change" gears.
you shift gears for tpi or feed. select either threading or turning.
you may turn at the same speed as you thread,
but unlikely.
typically you only "change" physical gears to go
from english to metric threading.

Jerry H
12-15-2016, 06:11 PM
This lathe probably does not have a full quick change gearbox. He will have to change the gear arrangement.

adamsgt
12-15-2016, 06:12 PM
to find the change gears, but I have what I should have for the Imperial leadscrew.
I have the following gears: 21,24,28,30,32,35,42,50,60,63,72. The 63 gear doesn't appear anywhere, even for the metric leadscrew, so, who knows what the precious owner used it for.

JerryH, thanks for nudging my memory I did that shortly after I got the lathe and forgot about it. So, I have the imperial leadscrew.

CMaier I'm still not clear on what the feed rate chart purports to show. The gear configuration in the feed chart is different from the gear configuration in the threading chart. I don't know if I'm stuck on stupid or what. Oh well, time to fix supper for my wife. She's kind of under the weather. I'll hit this again tomorrow. I'll just sit in front of the lathe and work the levers and see if I can make sense of it.

CMaier
12-15-2016, 06:37 PM
how about posting a pic or two of the front of the lathe ?
you should have a lever to select threading or turning.
and some way of selecting speed.
me thinks the chart is confusing the mechanical
part of your brain.
have a good dinner

adamsgt
12-15-2016, 08:47 PM
how about posting a pic or two of the front of the lathe ?
you should have a lever to select threading or turning.
and some way of selecting speed.
me thinks the chart is confusing the mechanical
part of your brain.
have a good dinner

OK, I found a picture on photobucket of the front of the threading gearbox that shows the three levers and their positions identified. In the user manual there is a drawing of this and it has arrows that point to all three levers and says "Feed and Threading Change lever". Notice that is says "Lever" when it points to three levers. Anyway, here's the picture:

http://i248.photobucket.com/albums/gg182/adamsgt/DSCN0654.jpg (http://s248.photobucket.com/user/adamsgt/media/DSCN0654.jpg.html)


There is a threading spindle and a turning spindle and a third rod that turns the main spindle on/off and controls direction of rotation.

A little more perusal of the feed chart indicates that for all feed rates the RST lever would be set to R and the other two levers would be set to 1,2,3,4, EorF to give the feed rate indicated in the chart. Again, predicated on the gear configuration indicated on the feed chart. So, if I didn't change the gear configuration from N on the threading chart I would just get an unknown feed rate. There is probably some way to calculate the feed rate from the threading configuration, but that's way beyond me.

At this point I need to either have a drink or go to bed. Maybe I'll do both.

Jerry H
12-15-2016, 09:22 PM
All three of those quick change levers control the eventual ratio of carriage movement to spindle rotation in conjunction with the outboard manual change gears. You are right in that the STR lever is always at R for turning. I don't see another lever to select the lead screw or carriage drive rod.

adamsgt
12-15-2016, 09:48 PM
All three of those quick change levers control the eventual ratio of carriage movement to spindle rotation in conjunction with the outboard manual change gears. Note that the STR lever is always at R for turning. I don't see another lever to select the lead screw or carriage drive rod.

There is a threading lever on the saddle that engages the leadscrew. There is also what is called an "Infeed lever for feed spindle" Down engages longitudinal movement and up for cross travel. So that must be what you're referring to.

The last time I contoured a barrel from a blank was in 1983 on a belt driven Southbend lathe. I was putting a 7mm Mag barrel on a 98 Mauser action. That was a lot easier than this. Well, if I ever decide to contour a barrel again I'll know what I need to do to get the nice feed rates for doing that.

Jerry H
12-15-2016, 10:02 PM
It looks it was designed for the easiest way to change thread pitches rather than feed rates. The fact that it doesn't have a "full" quick change gear box like the old SB lathe is what makes it laborious to deal with. I think the set up N when used for turning will result in a less than desirable surface finish when turning. The outboard gearing combos do seem odd for a manual change setup, particularly that 85/91 gear.

adamsgt
12-15-2016, 10:44 PM
It looks it was designed for the easiest way to change thread pitches rather than feed rates. The fact that it doesn't have a "full" quick change gear box like the old SB lathe is what makes it laborious to deal with. I think the set up N when used for turning will result in a less than desirable surface finish when turning. The outboard gearing combos do seem odd for a manual change setup, particularly that 85/91 gear.

Yeah, everything seems to spin off that 86/91 gear. Oh well, it is what it is. I'd dump it except that I've Bison D1-4 collet and set-tru chucks for it and other tooling. Besides I'm 76 and that's too old to spring for a new lathe. Ain't got that many years left, rather spend them at the range.

CMaier
12-15-2016, 11:50 PM
i have seen similar "lack of operating" instruction manuals.
technical data, but really light on the actual how to.

so chuck up some al stock and start playing with the machine.

i have access to a metric/english in one gear box lathe.

running it was the only way.
like you said it ain't like a south bend.

adamsgt
12-16-2016, 10:26 AM
i have seen similar "lack of operating" instruction manuals.
technical data, but really light on the actual how to.

so chuck up some al stock and start playing with the machine.

i have access to a metric/english in one gear box lathe.

running it was the only way.
like you said it ain't like a south bend.

Picked up some barrel blank drops from one of Shilen's swap meets and I'll use those to play with the gear configurations and see what kind of finish results I get. Interesting thing about the two charts. The finest thread shown is 112 which is .0089. That is about the middle of the feed chart. I'll have to see what that looks like on metal.

brickeyee
12-16-2016, 03:46 PM
And a pile of change gears for metric threads.

adamsgt
12-16-2016, 05:18 PM
And a pile of change gears for metric threads.

Actually, according to the charts, I have the correct gears to cut metric threads. However, I can't think of any reason why I would want to do so. I mean, English threads are hard enough. Besides, I never learned to speak metric.

Pete Wass
12-23-2016, 03:03 PM
OK, I found a picture on photobucket of the front of the threading gearbox that shows the three levers and their positions identified. In the user manual there is a drawing of this and it has arrows that point to all three levers and says "Feed and Threading Change lever". Notice that is says "Lever" when it points to three levers. Anyway, here's the picture:

http://i248.photobucket.com/albums/gg182/adamsgt/DSCN0654.jpg (http://s248.photobucket.com/user/adamsgt/media/DSCN0654.jpg.html)


There is a threading spindle and a turning spindle and a third rod that turns the main spindle on/off and controls direction of rotation.

A little more perusal of the feed chart indicates that for all feed rates the RST lever would be set to R and the other two levers would be set to 1,2,3,4, EorF to give the feed rate indicated in the chart. Again, predicated on the gear configuration indicated on the feed chart. So, if I didn't change the gear configuration from N on the threading chart I would just get an unknown feed rate. There is probably some way to calculate the feed rate from the threading configuration, but that's way beyond me.

At this point I need to either have a drink or go to bed. Maybe I'll do both.

Does anyone know of a source to buy the trim nuts that hold in the jog switch and light on the lathe in this picture? I have one like it with those two trim nuts broken.

Thanks,

Pete