Thread: C2 P.O.S lathe taper cuts

Take a nice deep breath It will likely all turn out ok in the end.

Are you turning near the chuck?
Are you using the tailstock?
What tooling and DOC are you using?
How did you level your lathe?

Stuart

Originally Posted by Stustoys

Take a nice deep breath It will likely all turn out ok in the end.

Are you turning near the chuck?
Are you using the tailstock?
What tooling and DOC are you using?
How did you level your lathe?

Stuart

Thanks for replying Stuart.
The pieces turned look like a top hat, I turned them within 20mm of the shoulder to the chuck, a tailstock was used with a replaceable carbide tipped cutter (10mm, unknown type) and DOC was about .2 mm, the swarf coming off was like steel wool. When it came down to size, several spring cuts were taken, eventually only dust came off. No power feed.
As the lathe is a 7" X 12", it is not bolted down, just sitting on a 19 mm ply bench top with 1 mm stainless on top. Plus, I find it easier to replace motors, (4 off them) as I can turn the lathe around on its bench to work on, far too often.
Kryn

Is the workpiece still in the chuck?

Did you try one without the tailstock?

Do you have any HSS?

Stuart

Originally Posted by Stustoys

Is the workpiece still in the chuck?

Did you try one without the tailstock?

Do you have any HSS?

Stuart

Hi Stuart,
I've taken the piece out of the chuck, as it was for a job, managed to get the taper out with a mill file. I do have several more to make, as these are parts for the Super Spreader I'm trying to repair.
I will do one without the tailstock to see what happens. I do have some HSS, but I don't know the quality of it, as I used some for fly cutting, on a block of 50 mm thick and 120 long MS (a pair of V blocks I'm making), after about 25 mm it was a resharpen job, it had 5% chrome moly on the bar.
Kryn

Hi Kryn,

Unless you are using high positive rack inserts, carbide might not do so well "sneaking up on size".

What size stock are you starting with?

Stuart

How long was the piece of material sticking out of the chuck?

I ask this as I don't really understand why ( spring cuts were needed ) , if you were using the tailstock for support.

Have you checked the amount of taper you have when turning between centres.

If you were to shim the headstock you would need to place the shim/s on the motor side, pushing the headstock towards the cross slide hand wheel.

Originally Posted by Stustoys

Hi Kryn,

Unless you are using high positive rack inserts, carbide might not do so well "sneaking up on size".

What size stock are you starting with?

Stuart

Thanks Stuart for replying. What are high positive rack inserts? I find using HSS is a pain in that it doesn't hold its edge for long, 5% crmo from LPR. Am starting with 25 mm bright bar.
Regards
Kryn

I know John upgraded his cross slide as he believed there was too much movement in the cutter head. I just sold John's to DaveTTC who is now living in Horsham, it will be there in by the weekend (hopefully). Perhaps you might arrange a visit to look at this and all the other upgrades John made to his

Kryn,
Have you tried chucking a length of ground bar in the lathe and running an indicator on that? If the indicator shows movement when the bar is rotated then it could be a chuck mounting problem (for example, back plate not perpendicular to the lathe axis). If you need to get that job finished sooner, send me through a sketch and I'll see what I can manage for you.

Michael

oops its "rake", others should be able to help............all the different inserts do my head in

I assume you mean 5% cobalt? It should be fine for turning 5mm off bright bar.

Hi Michael,
Chuck mounting shouldn't matter should it? wouldn't matter how much run out there is it should still turn without a taper.

Stuart

Originally Posted by Stustoys

Chuck mounting shouldn't matter should it? wouldn't matter how much run out there is it should still turn without a taper.

The lathe should turn without a taper (but it isn't, so...).
I'd be interested to know how well aligned the chuck is. Running an indicator along a reference bar may also show where the axis is pointed with respect to the bed.
Unfortunately I have Kryn's dial indicator here for repairs

Sudden thought - the (tapered) part has been produced by traversing the carriage along the bed and not just cranking the compound along hasn't it?

Michael

Kryn, there are so many possibilities for what may be wrong to cause your taper problem. Do you have the booklet "The Mini-Lathe" by David Fenner, it is number 43 in the Workshop practice series? There are a few good hints in there about this particular lathe, not too much about taper cutting though... Do you know this lathe comes with plain radial ball bearings made in China, and there are users upgrading this lathe (from standard noname 6202-ZZ) to good quality angular contact bearings (7206B-2RS) or even taper roller bearings (30206)? You cannot much pre-load plain radial ball bearings, and so there will always be some taper cutting as soon as you are taking more than a few hundreds of a millimeter depth of cut. How much I am not sure of, but something like 0.05mm over some 50mm out of the chuck does not seem that unreasonable to me (for an ordinary common China noname $3.75 each radial ball bearing I mean). Compare that to the price of a set P5 or better taper roller bearings as used on similar size quality lathes, such a set of two bearings can cost as much as your entire lathe with motor and toolpost included.

Me personally, I think that your taper cutting is unlikely to be due to a twisted bed. Because the bed of this lathe is very small/short, and such small lathes do not suffer nearly as much from bed twist as the slightly larger lathes do. For those unaware, the long bed Sieg C2 minilathe weighs only 37kg, swing over bed is 180mm, and distance between centers is 300mm. Just tad too fat for a watchmakers lathe. Also I doubt there is a major problem with headstock to bed alignment, although I cannot exclude the possibility. I just want to point out, that I would focus my attention first on the spindle bearings. Chris

PS: when checking spindle runout, your reference is the internal taper in the spindle. The low cost chucks sold with these lathes are known for having chuck body runouts of 0.2mm and more.

Keep in mind these lathes selll for under AU$700 with accessories such as 4way toolpost, variable speed motor, switched chuck guard, auto feed, emergency stop mushroom, 3-jaw chuck, live & dead center, metric changegear set, oil tray, 11 piece carbide tool set, quick change tool post with 3 tool holders and a steady rest all included. You cannot expect the accuracy of a toolroom lathe being thrown in as well for the same $<700.

Hell, nowdays $700 just about gets you one Kitchenaid mixer without much accessories beside a bowl and a couple beaters. If you want a juicer and a pasta roller and a mincer and an ice cream bowl with it, that is already twice as much money. Where is the relationship here?

http://www.ausee.com.au/shop/category.aspx?catid=49

miss alignment of the chuck will NOT make a taper
a bad quality chuck may do so
the jaws are supposed to hold the piece straight without movement
bell mouthed jaws will give a taper, so will sloppy ways the jaws run in
the deflection will be away from the force of the cutting tool
hence the taper will be bigger at the tailstock end

a cutting tool with the primary cutting edge perpendicular to the piece will minimize the radial pressure on the piece
and therefore minimize the deflection caused by the bad chuck and the deflection of the piece itself
a high positive rake, tiny front radius, cutting tool will make all the difference

that's where hss comes in...

Originally Posted by pipeclay

How long was the piece of material sticking out of the chuck?

I ask this as I don't really understand why ( spring cuts were needed ) , if you were using the tailstock for support.

Have you checked the amount of taper you have when turning between centres.

If you were to shim the headstock you would need to place the shim/s on the motor side, pushing the headstock towards the cross slide hand wheel.

Thanks pipeclay,
The piece was about 50 mm out from the end of the chuck, which is a Fueda, I believe to be a reasonable brand??
I did spring cuts as I was feeding this by hand not from the lead screw, just to take off any high spots.
Not done between centres yet, will try that this arvo.

Thanks Neil, will try that when I get a chance to get away.

Kryn,
Have you tried chucking a length of ground bar in the lathe and running an indicator on that? If the indicator shows movement when the bar is rotated then it could be a chuck mounting problem (for example, back plate not perpendicular to the lathe axis). If you need to get that job finished sooner, send me through a sketch and I'll see what I can manage for you.

Michael

Thanks Michael,
Will try that this arvo also. No real hurry for them, as I had to send the part out to a mates son , as I couldn't get it under my mill Thanks for the offer any way.

oops its "rake", others should be able to help............all the different inserts do my head in

I assume you mean 5% cobalt? It should be fine for turning 5mm off bright bar.

Hi Michael,
Chuck mounting shouldn't matter should it? wouldn't matter how much run out there is it should still turn without a taper.

Stuart

Hi Stuart,
Yes it is 5% cobalt. 5mm on that lathe, 0.5 more like it, it is a 7 X 12 after all.

The lathe should turn without a taper (but it isn't, so...).
I'd be interested to know how well aligned the chuck is. Running an indicator along a reference bar may also show where the axis is pointed with respect to the bed.
Unfortunately I have Kryn's dial indicator here for repairs
Sudden thought - the (tapered) part has been produced by traversing the carriage along the bed and not just cranking the compound along hasn't it?

Michael
Yes it was produced by traversing the carriage along the bed. I have a spare indicator anyway.
That is why my thoughts were that the head stock was out of alignment, the ^ not allowing the head to come back far enough.
Maybe need to look at getting an M2 test bar, to try it.

Thanks CBA,
I do have that book and will re read it again. The bearing upgrade was amongst the long term plans, IF it can keep it running long enough .

Thanks everyone for the help and suggestions, will try them this arvo/tomorrow.
Kryn