Thread: Hi-Torque Sieg SC2-L 14"x7" Dodgy Dovetail?? Advice needed.

Originally Posted by deppy

Hello there

A few months ago I purchased a Sieg Mini lathe for learning the art of machining. I am slowly tooling up and preparing some projects. I noticed that the tool holder rocks backwards and forwards when sufficient force is applied up and down on the tool tip. The tool tip will move about 0.5 mm up and down. I checked the jibs but no matter what I did no improvement was observed. I checked for burrs and found nothing unusual. Searching the web I could not find any reports of a similar problem. Then I noted that the compound slide makes contact with the top of the dovetail rather than the foot. At the foot there is a clearance of about 0.1mm. By comparison, on the cross slide there is a substantial clearance on the top of the dovetail and the slide rests on the foot...it seems to work ok. Does any one have enough experience to say which surface of the dovetail the slide should ride on? The current arrangement seems unstable and I am unable to machine anything other than with the slightest force.

Thanking in advance for any advice.

Ps I have contacted the ebay seller and am awaiting a reply.

I don't have the same model as you, nor am I familiar with 'lathe' terms. Also I don't 'recognise' your picture.

But for mine, a C3, when ever I experience play it is a long and complicated process to adjust. Adjustment is not intuitive. There are normally 3 hex screws with heads and two hex screws with the hex inset into the thread. the 3 work in opposition to the two to position the guide plate.

It cannot be done in situ and you must remove the slide, adjust the two inset screws, refit and try, if Ok .. then remove the slide again and tighten the three against the two.

If this sounds like gibberish I'm not surprised .. haahaa .... let me know and I will draw a graphic or photograph mine.

I have even had to cut down an Allen key to reach one adjuster screw as the one supplied could not get 'in' the space.

Having said all that, once adjusted, oiled and tight the lathe runs like a dream. But I only turn brass and wood .. no steel so far. I wash, oil and clean it after every session.

Hope this helps a bit ?


Also a question for any of the metal work guys: How far below dead centre should the cutting tip be ?

Greg

Originally Posted by deppy

................. Does any one have enough experience to say which surface of the dovetail the slide should ride on? The current arrangement seems unstable and I am unable to machine anything other than with the slightest force.

I never had a Sieg lathe. But I can say categorically that the contact must NOT, never, be at the single center section. Contact has to be at the two outher surfaces. Like you describe on your cross slide. In your case, it looks very much like the upper and lower part of the compound have been mixed up after the lathe was manufactured and tested at the factory. Try to persuade the seller to exchange the entire compound rest. Only if unsuccessful, should you consider fixing the mess yourself. The first step of a fix is, to mill off the top of the lawer compound casting. You want a gap of at lease 0.5mm there to the upper casting. Chances are this will fix the problem. If you want to be sure, use some blueing paste (as used for scraping) to see how the two side surfaces "carry". You want the surfaces to be in one plane. If they make only strip contact, you may have to correct with a dovetail cutter. Or get a crash course at scraping.... In any case, do not be tempted to use emery cloth or any "lapping" technique, that would only make things harder to fix. Chris

Originally Posted by cba_melbourne

I never had a Sieg lathe. But I can say categorically that the contact must NOT, never, be at the single center section. Contact has to be at the two outher surfaces. Like you describe on your cross slide. In your case, it looks very much like the upper and lower part of the compound have been mixed up after the lathe was manufactured and tested at the factory. Try to persuade the seller to exchange the entire compound rest. Only if unsuccessful, should you consider fixing the mess yourself. The first step of a fix is, to mill off the top of the lawer compound casting. You want a gap of at lease 0.5mm there to the upper casting. Chances are this will fix the problem. If you want to be sure, use some blueing paste (as used for scraping) to see how the two side surfaces "carry". You want the surfaces to be in one plane. If they make only strip contact, you may have to correct with a dovetail cutter. Or get a crash course at scraping.... In any case, do not be tempted to use emery cloth or any "lapping" technique, that would only make things harder to fix. Chris

Chris has covered it all there, see if it can be exchanged like he said.

Dave

A little bit more from me. I may be incorrect as my lathe is not in front of me.

But from memory, and mine is different remember.


But here is how mine works, it has 5 set screws for positioning the guide plate, in three dimensions, tho I have only drawn one.

It appears in your photo that the plate is missing ?



If you look carefully at the 'blowup, is that the head of a screw I can see on the right where my drawn thread ends ?

Hope this helps a bit.

greg

Just adding to Chris's comments...

If you can't do a deal with the seller, your best bet would be to if you can find someone with a surface grinder to help out.

Regards
Ray

Originally Posted by cba_melbourne

But I can say categorically that the contact must NOT, never, be at the single center section. Contact has to be at the two outher surfaces.

Never is a long time, there are dovetails the slide on the surface I belive. (if you mean never on one that small you maybe right)*

Some pictures on the flat ways would be good. I would have thought if both those surfaces were just roughed(as you would expect on a "normal" slide) winding the screw would feel like stirring rocks??

Stuart

*p.s. I think you are likely correct in this case, I'd just like to see the pictures to be sure

Originally Posted by cba_melbourne

I never had a Sieg lathe. But I can say categorically that the contact must NOT, never, be at the single center section. Contact has to be at the two outher surfaces. Like you describe on your cross slide. In your case, it looks very much like the upper and lower part of the compound have been mixed up after the lathe was manufactured and tested at the factory. Try to persuade the seller to exchange the entire compound rest. Only if unsuccessful, should you consider fixing the mess yourself. The first step of a fix is, to mill off the top of the lawer compound casting. You want a gap of at lease 0.5mm there to the upper casting. Chances are this will fix the problem. If you want to be sure, use some blueing paste (as used for scraping) to see how the two side surfaces "carry". You want the surfaces to be in one plane. If they make only strip contact, you may have to correct with a dovetail cutter. Or get a crash course at scraping.... In any case, do not be tempted to use emery cloth or any "lapping" technique, that would only make things harder to fix. Chris

Thank you Chris (and to all those who contributed). I am trusting that the supplier will see the defect and replace the assembly, as the modifications are beyond my present skills.

Regards Deppy

An answer for Greg. The cutting tip should be on dead centre. While the lathe may cut with it below dead centre it can cause problems and is to be avoided.

Michael

Originally Posted by Stustoys

Never is a long time, there are dovetails the slide on the surface I belive. (if you mean never on one that small you maybe right)*

Some pictures on the flat ways would be good. I would have thought if both those surfaces were just roughed(as you would expect on a "normal" slide) winding the screw would feel like stirring rocks??

Stuart

*p.s. I think you are likely correct in this case, I'd just like to see the pictures to be sure

Stuart, I meant "never" on a lathe. Lathe dovetails need to be first and foremost rigid, and low profile to maximize "swing over cross slide". Both requirements call for dovetails to carry on the outside surfaces. Chris

Originally Posted by deppy

Thank you Chris (and to all those who contributed). I am trusting that the supplier will see the defect and replace the assembly, as the modifications are beyond my present skills.

Regards Deppy

There is a booklet in the "workshop practice series" dedicated exclusively to the Sieg minilathe. It's issue number 43 by Dave Fenner (ISBN 978 185486 254 9). I bought it just for interest (I do not own a minilathe). It does not deal with your acute problem... but I can recommend it to anyone that just bought a minilathe as his first lathe. Chris

Originally Posted by Michael G

An answer for Greg. The cutting tip should be on dead centre. While the lathe may cut with it below dead centre it can cause problems and is to be avoided.


Michael

thank you Michael .. I have been shimming just below .. But will bring it up to dead centre .. Much appreciated

Greg

The Mini lathe shop in the USA has excellent tips for the minilathe as well as spare parts. Apparently a bit of work is required to set up the machine to its best, there is also a SEIG forum apparently.
Kryn

Dear Metalwork Forum
The ebay seller sent my query to their Chinese supplier who responded suggesting I grind or scrape the top of the dovetail 0.3mm, which is pretty much what Chris suggested. Fine, if you have access to a surface grinder (which I don't)...but the jib strip also needs to be re-machined as the dimples are far off from the screws enough that they cannot engage with eachother. (The machinist who made this part must have had a bad day). The screw's thrust bearing may also need be modified as the adjustment will change its height. Given that I don't yet have the expertise or the equipment to make the modifications, I have asked the seller for a replacement compound assembly. For now they have forwarded my request to their supplier. I will let you know of the response. If negative, I will reveal the seller so that others may be aware of the potential pitfalls of purchasing such a machine online. So far they have been responsive, but reluctant to provide a resolution themselves.
Cheers
Dennis

Originally Posted by deppy

Dear Metalwork Forum
I will reveal the seller so that others may be aware of the potential pitfalls of purchasing such a machine online. So far they have been responsive, but reluctant to provide a resolution themselves.
Cheers
Dennis

Sieg have always marketed their machines as a cut above the average Chinese lathe, and asked a higher price, but in reality they are no better and may even be worse than many no name brands. You are not the first to buy the red machine and have problems.

The finish of that topslide is truly awful when one looks at the malformed gib strip and the hopeless dovetail alignment.

Says it all.

Good luck with your supplier, I hope you get satisfaction.

Rob