Lathe carbide tool issue

Hello all,

I’ve been having an issue with a 3/8” right hand carbide tool holder(carbide bit is held with one small torx screw) being used on a Sherline 4410 lathe.
I acquired the carbide tooling to assist in turning Titanium Grade 5 - TI6AL4V pivots, roughly 12mm diameter to required size. The lathe has a DRO which displays to 0.01mm on both axis(calibrated to the machine and compensated for backlash).
The issue is when using the carbide tool for example if the part is if I adjust the cross slide to remove 0.2mm depth of cut(0.4mm total material removed) it’s only removing approximately half of that amount I.e 0.1mm depth of cut, 0.2mm total material removed, the amount removed always seems to vary and is never a consistent error.

I’ve used a HSS 1/4” tool and there is no issue, my question is there something that I need to do different with the carbide tool? Thanks

Hi Karl,

Welcome to the forum. Carbide tooling needs a rigid lathe, high speed and a certain depth of cut, usually at least the nose rasius of the carbide insert. I often use carbide for the roughing cuts and finish ith a newly honed HSS tool.

Thor

+1 for what Thor says about needing a certain depth of cut and a machine of sufficient rigidity to hold the tool into the cut.

As you probably know titanium can be a right pain to machine. Best practice would be to stick to "book" feeds and speeds using an insert specified for use on titanium. Dont know if your little Sherline can reach book values. Its asking a lot of a baby lathe.

I see Sherline advise the use of HSS tooling **LINK**

https://www.sherline.com/sherline-videos/test-cuts/

A good quality, Sandvick, insert intended for the more obdurate range of steels did not do well for me when I discovered that the handy bit of metal the right size was actually titanium! Didn't know I even had any titanium!

Clive

Edited By Clive Foster on 12/09/2022 08:46:55

Most carbide inserts are relatively blunt compared to a well sharpened piece of HSS so need a decent depth of cut to work well. Going for a small cut will probably result in the tool randomly going between rubbing and cutting and so produce a terrible looking result. A carbide insert sharpened and polished for use on aluminium is a much better option for small cuts than the standard inserts. They are also good for use on other materials if you have a rigid lathe, I have used them to machine stainless steel and HSS.

So the issues you are having are probably due to the type of insert you have has a relatively blunt cutting edge and the lathe is not rigid enough to resist the forces that result from this bluntness.

Martin C

Carbide inserts are available in a very wide range of shapes and materials. Polished, un-coated tips are often specified for aluminium and difficult metals. They are usually very sharp and quite delicate and can make fine shaving cuts as well as general turning with a fine finish in my experience. I suggest that choosing the correct grade of carbide will solve Karl's problem.

HTH,

Rod

Agree totally with the reponses so far. A Light machine like the Sherline is not optomised for tools like this in my opinion. Good HSS bits will give much more consistent results. Cutting titanium on such a machine is probably pushing things, I'm sure it is possible, but never going to be easy.

regards Mike

Sounds like deflection because the tool isn't sharp enough

You can sharpen/dress carbide with a green grit wheel, leave plenty of support under the tip

Easiest solution is HSS/M35 but if you can suss out a good carbide system it cuts forever compared to hss

Hi all,

Thanks everyone for their input, it’s much appreciated!

I can now see the rigidity and shape of the tip definitely being an issue, it makes sense because when using the carbide tool it takes a fair bit of pressure when feeding it to cut. On the other hand with a newly sharpened HSS tool it it’s a very smooth and continuous cut with no strain on the machine even though it’s titanium. In terms of speed I’ve been calculating the rpm based on the sfm for the material and it’s diameter(there’s another number in there too that I can’t mind off the top of my head) which has worked well for all the other materials I’ve machines on it, even some stainless steel.

The main reason I was trying to use the carbide tool was the longevity of it, as much as I enjoy sharpening HSS tools I thought it would be more economical with my time to use carbide. As mentioned it may be the wrong type/shape?

I think I have a 1/4” brazed carbide tool floating about somewhere that’s as sharp as the HSS one, may be a better option than the insert type hopefully. Failing all that I’ll just need to stick to the HSS as Clive’s link shows.

Will let you know if I succeed!

Regards,

Karl

Hoi Karl. Stefan Gotteswinter shows how to sharpen carbide tips on his excellent YT channel.

Carbide sharpening. Well worth taking the time to watch.

regards

Yes, and IIRC, Sumitomo do titanium carbide inserts which claim to be suitable for small DOC.

You don't say the size or shape of your inserts but one on the **GT inserts for high temperature alloys (not aluminium alloys) is what you need and they will take light cuts, something like this

The rated power of your motor is I think 90 w and that is very small to consider any form of carbide tooling. If you are successful with HSS, you should stick with it

Grinding HSS tools is very easy with a grinder and fine wheel I’ll add photos of my setup later simple to build it uses the radius of the wheel to provide front and side clearance when the holder is on the sliding platform. Although I have a tool and cutter grinder, this set up is used for all but very critical grinds as it’s so quick to use. One of these days I’ll make a metal base fir it as the sliding part tends to stick a bit removing some sensitivity.

The Sherline will be fine with suitable Carbide, look at the work from the likes of Chris Rueby almost all done with carbide

Edited By JasonB on 12/09/2022 13:04:46

The critical dimension is the platform top should be 10 mm below the wheel centre the slider with the adjustable angle is 6 thick, and the tool holder is 8 mm thick . Note the tool is located by a 6 mm square riveted to the base , and is sized so the tool is able to be located on the front or side Springs push the top plate up to release it when the wing nuts are loosened.

I also have holders for small round shanked preformed boring bars and other round tool bits

Jason, yes I agree about some can work well with carbide with this lathe, but I was echoing earlier posts about the lack of power, its lack of rigidity and the op had success with HSS

Edited By Zan on 12/09/2022 13:30:32

The above is the way to go, carbide shaped like hss, just don't stall the cut.

Brazed carbide requires power and speed, which gives the heat to cut. OK on steel with big depths of cut, but not so good for a Sherline.

With a smaller lathe, the inserts designed for aluminium used with small depth of cut would be my choice, I use them for finishing cuts on steel and have also used them on titanium aircraft parts, we have plenty of spare bits waiting to be made into something else at the museum.

If your inserts are identifiable, you can get certain types in pairs rather than boxes of ten from APT, which is a good way to experiment.

Edited By old mart on 12/09/2022 14:22:43

First off, thanks to you all for your contributions, photos and links! Really insightful to a novice. Great community of members!

A bit of information regarding the actual carbide: it’s supplied by Sherline it’s their 55 degree carbide insert, it’s a gold colour(7605B this is the part number for it on their site which has the radius, angles etc) This is mounted in a Sherline RH 3/8” carbide insert tool holder and in turn is secured in a Sherline 3/8” toolpost. So all offered by the manufacturer for the machine, which made me assume it could be used within the limits of the machine and I had it purposed specifically for turning titanium and to save on sharpening HSS tools.

Hope the information on the bits gives a better idea.

Regards,

Karl

That is a ANSI code for a DCMT insert which are the "blunter" types, The one I linked to earlier will be a direct replacement and is one specifically for Titanium alloys. It has a smaller tip radius and is also meant for fine finishing which will be ideal of the Sherline

As a half way house you could get away with a similar general DCGT that is not specifically for titanium such as this which can be had in packs of two

What part of the world are you in? as that will affect availability of what is suggested

Edited By JasonB on 12/09/2022 14:58:15

JasonB, I’m in the UK.

Regards,

Karl

The APT ones will do you then, It's just that the titanium specific ones you will probably have to get a box of 10

The ones for aluminium, non ferrous and Stainless will also work well on steels too and I would suggest using them for all your turning and they may well do for the titanium too. Worth a try to just buy two of those. This is one taking a 1thou (0.025mm) depth of cut on steel

Edited By JasonB on 12/09/2022 15:13:46