Sieg C1 lathe autofeed and screw cutting

[Howard LewisParticipant @howardlewis46836]

As already said, if screwcutting (As opposed to using Taps or Dies) the leadscrew must not be disengaged from the gear train, so do not disengage the dog clutch, whether stationary or in motion.

If it is, the relationship between the cutting tool and workpiece will be lost. It will be very difficult, if not impossible to reestablish it

Although winding to and fro, with a mandrel handle, for working up to shoulder, or down a blind hole can be a pain, it is better than the risk of broken Taps, or stripped threads, for a scrap job!

For screw cutting, rather than using a Tap or a Die, the gear ratio used will determine the movement of the Saddle relative to the workpiece in the chuck.

The slower that the Leadscrew screw revolves, relative to the chuck, the finer will be the pitch of the thread, or conversely, faster equals coarser pitch thread.

With only 150 watts available, large diameter, coarse pitch threads might be beyond the capability of the motor. And running at low speeds, the motor will not be passing much air through to cool it, so could over heat, if used in this way for long periods.

And I would not rely on the overload facility, too much. If, eventually the motor or control  board (possibly both!) need replacement, you are looking at at least £100+ each.

The C1 does not seem to be imported into UK any more, so spares might be hard to find, and harder as time goes on.

A few minutes, rotating by hand will be cheaper and more convenient!

Howard

[Howard LewisParticipant @howardlewis46836]

For auto feed, presumably to get the best surface finish, set up the gear train so that the Leadscrew revolves as slowly as possible, relative to the chuck.

In the case of the C2 and C3 mini lathes,the gear set enables a train of 20:80/20:80 to be set, so that with a 16:1 reduction and a 1.5 mm pitch leadscrew, the feed rated is 0.09375 mm per rev. (0.0037″ in old money)

The 80/20 gears are compounded by means of a key connecting the two gears, on the stud.

It MIGHT be possible to use gears from the C2 and C3 on the C1 (They are Mod 1, and the bore and thickness might be the same)  to supplement those that you already have.

Spare gears are available, from importers, so measure one of your gears, and count the teeth.

The formula is          (Teeth+2) / OD in mm = Module

To see what is available take a look at the Arc Euro Trade website. (“C3 Change gears”) They list gears from 30 up to 80 teeth in 5T increments.  If you are unsure about dimensions of the C2 and C3 gears, ring or E mail. I am sure that they will be most helpful

Howard

[Howard LewisParticipant @howardlewis46836]

It looks as if the gears that you already have can be set up to provide a feed of 0.05 mm per rev, which is a fine enough feed to give a good surface finish with a sharp tool (preferably with a small nose radius) set on centre height.

So for auto feed, you may not need any extras. Just use a small depth of cut, and the fine feed.

For roughing cuts (Bear in mind the minimal motor power!) you can hand feed more rapidly.

But don’t over do the feed rate or depth of cut.

This is all part of becoming familiar with the machine, and how to use it.

Howard

[th1980Participant @th1980]

This lathe is a bit of an odd ball because the leadscrew is permanently engaged to the saddle. The clutch only connects the motor to the leadscrew. So position is impossible to loose while cutting threads. I’m not using the autofeed much (or at all really). Stopping the saddle takes as long as the chuck stops rotating after the power is swithed off (I don’t know if the clutch could be operated while under power). Moving the saddle long distance is a pain because you have to do it by hand cranking the leadscrew from the end of the machine.

If the control board breaks some day, I might be able to repair it myself.

I wont be buying the gears just now. I’ll need to research the topic further.

[th1980Participant @th1980]

And yes, there are gears already in the lathe that make two feed speeds possible. Stalling the motor has not broken anything in the lathe yet but the carbide inserts don’t like that very much….

[Howard LewisParticipant @howardlewis46836]

Bear in mind that the motor on a C1 is only 150 watts, so SHALLOW cuts, using the low feed rate, are the order of the day.

Keep the tools sharp and mounted on centre height.

Be content with 0.005″ (0.127 mm) cuts. ) 0.1″ (2.5 mm) are beyond the capacity of a C1.

You wouldn’t try using a 750 cc Reliant Robin to pull a trailer carrying 20 tons!

If you want 1/2″ a side cuts, find a 21″ Dean Smith and grace with a 20 hp motor!

[th1980Participant @th1980]

Bear in mind that the motor on a C1 is only 150 watts, so SHALLOW cuts, using the low feed rate, are the order of the day.

Yes, I know. I have had the machine for several years and this became evident right at the beginning. The lathe has a good motor control board that cuts the power if the motor gets even slightly overloaded.

I have now ordered the 9 gear set.

I used this online tool:

https://ridethegeartrain.com/

I inputted the relevant data for my lathe and got results that indicate that practically all the imaginable imperial threads are possible within 0.1% error using those 9 gears + the excisting gears already on the lathe. Except for a few of the very large threads that wont ever be needed. And all the metrics are possible within 0% error.

I do realize that not all the hypothetical gear combinations produced by the program are possible to actually implement on the lathe but this should still cover most of my needs in the future.

[Howard LewisParticipant @howardlewis46836]

With the extra gears all manner of thread pitches and feed rates become possible, so you will be well set up.

The chances are that the Leadscrew pitch will be 1.5 mm so the gear trains that can be set up on a mini with a 1.5 mm Leadscrew will work for you.

Good Luck!

Howard

[th1980Participant @th1980]

Thanks Howard!

The leadscrew pitch is indeed 1.5 mm (I measured it) although the manual incorrectly says it is 3 mm.

Now I have to buy some thread cutting inserts and a shank. Any recommendations? I’m going for the cheap Chinese variety, they have worked for me in the past…

[Howard LewisParticipant @howardlewis46836]

A Mandrel Handle might well be an item on the Round Tuit!

In this day and age, most threads will be Metric, so full form thread tips, and holders will be available.

I would probably contact JB Cutting Tools, for a start.

Other suppliers may be able to help. (RDG, Chronos?)

At a push, a triangular tip might get you by

Probably heresy, but with both being 60 degree form, a Metric tip could probably be used to cut a Unified thread.

For Whitworth form threads tools are probably available, but for BA (If you chose to screwcut rather than use Dies) you would need to grind your own tools.

Setting up a gear train for Metric threads should be fairly easy, but Imperial pitches will cause some head scratching, over compound gears, for instance. A 63T gear may help, although not without some errors creeping in. Unless the thread is long, possibly not large enough to cause problems.

Brian Wood’s Book “Gearing of Lathes for Screwcutting” may give an indication of how big the errors are for a particular set up.

HTH

Howard

[OldironParticipant @oldiron]

I have a C1 clone that I use very rarely. It is good for the really small stuff. Generally it gives a good finish to most materials.  HOWEVER  yesterday it started clonking and then the drive to the chuck stopped.  The belt had shredded itself.  Belt is 1.5 mod 10 x 395 mm with 83 teeth.  Looks like they are as rare as hens teeth. Sent out a few emails so may be lucky but if anyone has a spare they no longer need I would purchase it.  May be available from China but waiting for answers.  BTW the C1 has no halfnuts so I leave the lead screw engaged when threading with it due to the lack of a threading dial. You have to be real quick to stop the lathe when threading up to a shoulder. Also if you switch to reverse it turns every thing backwards including the chuck.

[JasonBModerator @jasonb]

That man Ali will send one express delivery. Search M1.5x83Tx9.5mm

[th1980Participant @th1980]

https://littlemachineshop.com/products/product_view.php?ProductID=5538

[BazyleParticipant @bazyle]

Oldiron, looks like you should be making a mandrel handle for threading which will also be useful for using taps and dies.

[Howard LewisParticipant @howardlewis46836]

Arc Euro list a belt for the C!, as a spare. C1-131 at £7.36 plus £3.50 carriage, but sadly out of stock!

Take a look at their website., for any other possible spares.

Since you have the details of the belt, you should be able to find one from a local bearing / belt/ engineering supplier.

Howard

[Martin of WickParticipant @martinofwick]

Best to bite the bullet and replace the oddball M1.5 weird stuff with something sensible and easily available like HDT M5 timing gears.

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