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gr8life
06-18-2010, 02:06 AM
Just curious how many members thread using the cross slide only vs. using the compound. I had to do some today and did it both ways just to see the difference. Don't want to make this a long discussion just curious.
thanks
ed

lakeside53
06-18-2010, 02:11 AM
I do both on my 14x40 lathe.

Crossfeed only - small threads and or easy materials (aluminum, 1144 etc).

Compound : bigger threads or tough materials (most stainless).

Sometimes I'll start with the crossfeed, and if the going gets tough.. switch to the compound.

Arcane
06-18-2010, 02:18 AM
I do the same as lakeside53. Since I have a 9"SB, my "bigger threads" start at a lot smaller size though than his I bet!

Mike Burch
06-18-2010, 06:51 AM
One disadvantage of the small Sieg C3 lathe with the DROs is that the compound can't be set around far enough for threading, as the DRO fouls the fixed bit of the cross-slide when the compound is moved more than about 20°. Hence, I can only use the cross-slide for thread cutting.
One of the advantages of the same lathe, though, is the electrical reversal, which means that I don't have to disengage the half-nut at the end of the cut. I just reverse the motor switch, and the leadscrew reverses (along with the spindle and chuck) and takes the cross-slide back to the beginning.

Evan
06-18-2010, 06:54 AM
I mostly use just the cross on my SB9. The really big advantage of the SB9 if it has the original motor is instant reverse. You can switch from forward to reverse while still running forward and it will stop within a couple of tenths of a second and start up in the other direction. And no, it has never unscrewed the chuck because of it. If used with good timing it makes it possible to thread right up to a shoulder as it can be used as a brake.

Richard Wilson
06-18-2010, 07:15 AM
[ The really big advantage of the SB9 if it has the original motor is instant reverse. You can switch from forward to reverse while still running forward and it will stop within a couple of tenths of a second and start up in the other direction.
I was interested in switching a single phase motor from forward to reverse to use in a drive for a small planer, but when I enquired on another site, I was told that it couldn't be done, and if you switched to reverse with the motor running, it would just keep running in the same direction. So, whats special about the original SB motors? Would they tolerate this happening every couple of seconds as in a planer drive? If so, whats the modern equivalent of the original SB motor?

Richard

J Tiers
06-18-2010, 09:23 AM
They are a repulsion type motor*, which is the only single phase that reverses well. (A PFC does reverse, but not as well).


* A "repulsion start" motor is not at all the same thing..... it runs as an induction motor, and won't reverse.


BTW, if you use the crossfeed only, on a lighter lathe, you may experience the thread "taking charge" and producing a drunken thread if the carriage gets "pushed ahead" by the thread being cut. With a RH thread, that side has the negative rake, and cuts worst..... making it more likely, especially with variations in the metal hardness, etc.

A heavy lathe has a heavy carriage, which is harder to push...... so it just cuts.

The advantage of the compound feed is keeping forward pressure, and tending to prevent the "taking charge" problem.

Nobody will ever believe that until they see it, so it always draw the usual "been doing it for years and never seen a problem" comments.... Then you may find out that they use a 20" swing lathe, and usually cut threads on 12mm workpieces.................... d'UH....

Boucher
06-18-2010, 09:31 AM
I normally use the compound for threading.

JoeLee
06-18-2010, 09:49 AM
I also use both when threadding on my Clausing 5900 depending on material toughness and thread size. Once you get your insert in the thread about 40% you may start to get some chatter, so that is where the compound slide comes in handy. You can start to flank each side of the thread untill the proper depth is reached.

JL......................

S_J_H
06-18-2010, 09:51 AM
Yeah for finer threads I use cross slide and coarse larger threads I'll use the compound.

My SB9 is fitted with a DC motor and drive. I once hit the brake switch with the spindle rpm a little to fast and off came my chuck and slammed into the wall.:eek:

I'm a weebit more careful now with braking and reverse on the SB9.;)

Steve

Dr Stan
06-18-2010, 11:14 AM
Like others I typically use the compound, but for pitches of 32 or finer I'll go with the cross slide.

Paul Alciatore
06-18-2010, 11:57 AM
On my SB I usually use the compound.

My Unimat does not have a compound and threading is done with a "chasing" attachment. The feed is straight in, just as with a cross slide.

Both seem to work OK.

Fasttrack
06-18-2010, 01:40 PM
+1 for Lakeside's method. Also, it depends on the cutting tool. The one exception is carbide. If I am using a carbide threading insert/brazed carbide tool then I *always* use the compound. Took me several chipped tools to learn that lesson. But I use HSS almost exclusively, so usually I make the decision based on how fine the thread is and which machine I'm on. My Pacemakers don't seem to care one way or the other, but feeding with the compound tends to produce a cleaner thread.

Black_Moons
06-18-2010, 02:11 PM
Yea.. Capacitor start/run motors reverse.. Just not untill the RPM's drop low enough for the centrafugal starter switch to reengage the starting coil.
I wonder if it would be possable to make a system that overrides the centrafugal starter switch when you try and reverse it?

bborr01
06-18-2010, 02:35 PM
I only use the compound for advancing the tool bit for threading.

Compound set at 30 degrees.

Bring tool bit close to the workpiece.

Set cross slide dial to "0".

Start threading, advancing the compound on each pass and backing the tool bit out with the cross slide at the end of each pass.

Advance cross slide to zero again and advance compound on each pass until you have the right depth on your thread.

I learned this method of threading from a group of about a dozen full time lathe operators and they all did it the same way.

That is not to say there are not other ways of threading.

But I figured why argue with tens of thousands of hours of experience.

Brian

John Stevenson
06-18-2010, 02:46 PM
Now I have made it I use that swing threading tool for everything.
Really speeded things up for me.

Just the cross slide, no compound on the small TOS.

.

Carld
06-18-2010, 05:24 PM
I always cut threads with the compound, fine or coarse. Having thought about it a lot I prefer the cutter cutting on the leading side rather than both sides.

The times I experimented using the crossfeed only I was not pleased with the results. fine threads are best cut in one or two passes.

Do it your way, you'll like it better.

Ron of Va
06-18-2010, 05:40 PM
I am an amateur and do mostly fine threads. When I first started, I took a machinist advice, and bought full profile inserts. I tried using the compound, and had poor results. (I don’t think I stuck with it long enough.)

I started using the cross slide while the compound was at 90º to the cross slide and started having much better results using full profile inserts. (I used the DRO to get to the exact depth.)

J Tiers
06-18-2010, 10:59 PM
Yea.. Capacitor start/run motors reverse.. Just not untill the RPM's drop low enough for the centrafugal starter switch to reengage the starting coil.
I wonder if it would be possable to make a system that overrides the centrafugal starter switch when you try and reverse it?

yes there is such a system, and I think it may have been the subject of a thread here some months ago. It involves an extra relay, and some other things I don't recall.

The essential feature IIRC is that it plops the cap in-circuit to start the opposite direction to the existing rotation. Kinda rough on the cap, but with correct rating can work.

boslab
06-19-2010, 12:40 AM
i
I mostly use just the cross on my SB9. The really big advantage of the SB9 if it has the original motor is instant reverse. You can switch from forward to reverse while still running forward and it will stop within a couple of tenths of a second and start up in the other direction. And no, it has never unscrewed the chuck because of it. If used with good timing it makes it possible to thread right up to a shoulder as it can be used as a brake.
i still find it nervewracking to say the least, id rather a coward trench at the end of the thread if i can, its an odd thing that SSS lathes didnt really develop more screwcutting features over the years like an adjustable dog clutch or somthing to aid screwcutting.
I often get to do internal blind large diameter [3" BSPP] screw caps in soft ****ty ali, ive broken quite a few boring tools aka internal threadcutting tools.
perhaps there is a better way without a cnc but i havent found it yet.
so much to learn so little time
mark

Vern2
06-19-2010, 01:37 PM
I've not had any success threading. Bought another lathe to see if it helps. I sent back a Sieg 9x20 and have a 12x37 in the shop to put together. Been getting threads close and running a die over them. What a pain with 7/16 - 14. Only been at this for 3 months. This lathe has a bump button, plus reverse, don't know it it will help. Tried compound, threads were too short and to far apart, probably using wrong angle. The only luck was to leave the half nut in and turn motor on and off, the nut still would not screw on.

Vern

Tony Ennis
06-19-2010, 02:04 PM
Vern, have you read up on making threads?

If so, have you checked your machine to make sure it has the expected leadscrew pitch and so forth?

Mike Burch
06-19-2010, 09:26 PM
Vern, despite the misleading publicity, the Sieg lathes do require different leadscrews for metric and Imperial threads. If your Sieg won't cut a 7/16" x 14 thread at the correct TPI, you might have a metric leadscrew fitted.