Chatter/finish problem

The U tube lathe does not seem to have a slit bearing, but wether it should is debatable.

At this sort of age it's unlikely any survivors have not been modified in some way. I have a T&LM that has slit bearings similar to a collet and the threaded ring is used to adjust the running clearance. The slit also serves to hold a felt wiper that rubs against the shaft. The end float is controlled by a brass washer behind the chuck mount flange however this doesn't really work for cutting toward the tail stock.

Can you confirm that those marks appeared during a single direction cut and you didn't back it out the same way as you went in? They look to be like a coarse thread like I get when winding out much faster after a cut with some spring in the tool.

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I’m back

That new picture makes much more sense than the one that I was commenting upon earlier

… You actually have something appropriate against which to adjust the collar

… Go for it !!

MichaelG.

Ok, I reassembled it all and put a little grease on the collar thing, tightened it and now there is no discernible longitudinal or lateral movement.

I made another test cut, see below, the middle section, and it’s way better, still bad, but consistently bad rather than having diagonal lines and random scratches all over it.

I think your tool may have too much of a point and/or your feed rate is way too fast. You're basically creating a screw thread. Have a look at this video by Joe Piecynski about surface finish.

Links to https://www.youtube.com/watch?v=-mNH1ZLy-hk

Rob

You might find this link useful:

**LINK**

http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm

Russell

Edited By Russell Eberhardt on 27/09/2021 19:12:36

Have a look at the workholding ,is the bar held firmly in the chuck jaws? From the photo the new chuck appears to be a self centering 4 jaw chuck, not the best way to hold work, I would never dream of using this type of chuck they are ok for woodturners. Never seen one used in a trade shop. And do not assume that a new chuck has perfect jaws to grip the work along the length of the jaws, I have seen a new european made 6 inch 3 jaw chuck where the jaws were bellmouthed ,due to poor manufacture. The tool looks suitable for brass ,though is there sufficient front and side clearance plus tools for brass turning must be sharp and honed with an India oil stone,some grades of brass can be difficult to turn and get a good finish, try going fast in top speed and take cuts of around 5 thou.The very rough cuts look as though they have been taken at very slow speed with tool set to take a far too great a depth of cut, like screw cutting to full depth at one cut only worse,that will not do the lathe much good.

David Wilkes in his You Tube videos preferred turning toward the tailstock. He turned some really long slender shafts without chatter.

Unless I'm not seeing clearly, the tool appears to have a short area of negative rake. If this is the case, whilst it reduces or eliminates the risk of dig ins, it may not be the ideal geometry for turning brass.

FWIW, my method would be, for brass, a knife tool with zero top rake, and to wind the tool out before winding the saddle back. Front and side clearances are necessary, but only about 5 degrees

(That coarse helix does look like the Saddle being wound back while the work was rotating. )

Are you hand or power feeding?

If the lathe has a Leadscrew, the changewheels / gearbox can be set to give a fine feed of 0.004" / 0.05 mm per rev. If the tool geometry is correct, and mounted on centre height, that should result in a good finish on brass.

You will need to calculate the gear train to give 250 tpi, or 0.05 mm pitch for the fine feed. As aleady said, you are producing a screwthread of fine pitch.

The finishing cut needs to be shallow, especially when using HSS tools, probably of the same order as the feed rate, or maybe less..

Being brass, it is taken that no coolant / lubricant is being used.

HTH

Howard

Side note to John Reese - I haven't seen any new videos from David Wilks in a very long time. Do you know David, and if so, is he OK? I think he is from Sheffield.

Never understood 4 jaw self centering chucks. As they work on a scroll all 4 points of the jaws are unlikely to be truly on a circle, and not all round bar is perfectly round, so chuck is likely to just grip on 2 opposite jaws. That's why self centering chucks traditionally have 3 jaws, 3 points always define a circle, and will cope with slightly out of round bar

It is a 4 jaw independent chuck

Well, I ground my first HSS cutting tool. Is that right? Luckily I have suitable kit to do that due to my woodworking habit. I’ll give it a proper test after work.

Steve

Edited By Steve355 on 28/09/2021 14:15:00

From your photo it looks wrong, but if the point of that little triangle is not as far out as it's base (top of tool) then it will work. A rounded edge would be better.

PS I've never seen an HSS blank that didn't have polished sides.

Edited By Dave Halford on 28/09/2021 14:40:41

For some reason when I post pics here they are rotated through 90deg anti-clockwise, if you rotate it through 90 deg clockwise then that’s how the pic should look.

it’s not an HSS blank, it’s the rear end of another tool that I have re-purposed. I have ordered some HSS blanks but they don’t arrive until Friday.

It's not the rear end of a brazed carbide tool is it?

Regarding rotation of photos, it's a continuing problem on here - done it myself - and it seems that one way to fix it is to open your photo in a photo-editing program and re-save it before posting.

No, it’s the other end of the HSS tool shown in an earlier picture 😎

That's OK then

I get the rotation, it's the little flat that you ground on the point to widen it looks to have no clearance

Agreed. It will in fact give a severe negative rake to the cutting point.

If you want to have a small flat, or a rounding, on the point it should be ground all the way down the leading edge.  The top of the tool must remain flat.

Russell

Edited By Russell Eberhardt on 28/09/2021 19:03:17

Right, thanks for all the help from this excellent forum, I think I’m starting to understand some of this. I think there are actually three problems:

1) a problem With the collar at the tail end of the spindle, looseness was causing longitudinal movement of the spindle. I think I have fixed that.

2) A problem with tooling, resulting in the finish being a “long thread” when tail support is applied. The tail support would also stop any longitudinal movement of the spindle. I will re-grind the tool tonight and give this another go.

3) I have also noticed that in order for the spindle to turn, the bolts that secure the spindle in the headstock need to be only slightly more than finger tight. Whilst it seems that there is no lateral movement on the spindle, if I pull the spindle with a little force, I can feel the headstock slots flexing. So therefore there must be very little rigidity, and it may explain The test cut I did last night, where on an unsupported pace the finish is horrible further out, improving markedly closer to the Chuck.

But if I tighten the headstock bolts, the spindle will not turn. A couple of questions:

Does this make sense? Might this be a problem?

What tension should the V-belt be? Is there any way I can measure it?

It’s a basic cheapo eBay V-belt. Is this the wrong kind of belt? I have seen a myriad of different belt types on lathes.co.uk.

I will get to the bottom of this!

cheers

Steve