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Is buying a custom ground tool my only option??

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Guy Thornhill30/06/2021 17:53:49
3 forum posts

I have a need to machine on my lathe effectively the groove geometry typically seen on a deep groove ball bearing. The reason that I can't just buy a bearing is that it is a large diameter of around 100mm and low profile, balls 5 or 6mm in diameter.

The bearing won't be under any heavy loading so no safety concerns but it does need to run smooth with friction kept to a minimum. Material is likely to be free machining steel.

Both the internal and external rings will fit on my lathe but I'm struggling to work out what kind of tool to use for turning the groove. I can't find anything standard and I don't think I'll be able to grind anything nearly accurate enough with my grinding set up.

Does anybody have any experience or suggestions of doing something similar? All I can think of is that I'll need to organise a custom tool being ground up by a toolmaking company. What would a reasonable price be for a pair of tools to turn the internal and external groove?

Any advice would be more than welcome.

JasonB30/06/2021 18:21:06
23022 forum posts
2763 photos
1 articles

If you went with 5mm balls you could consider a grooving insert such as this and a suitable holder for the internal groove. If your lathe will run in reverse then the same tool can be used at the back of the work to do the external groove if not you will also need an external holder.

You will need a rigid machine as the cutting width and 100mm dia will cause chatter on a light machine.

A template and copy setup may be another option.

Dave S30/06/2021 18:30:34
373 forum posts
90 photos

Could you get away with a V groove? You’ll end up with a line contact on the balls, but that may be sufficient for your application. Grinding a V to suitable accuracy should be no harder than a threading tool.


old mart30/06/2021 18:33:43
3886 forum posts
264 photos

Welcome to the forum, Guy, what you are up against is the great difficulty of turning a round groove which is one of the most difficult things to do without chatter. I have tools using round inserts of diameters from 6mm to 20 mm, but have never succeeded in getting the required finish in a turned groove. I would think that your best bet is finding a bearing that is near the size and getting the races ground as there will be some wall thickness available for modifications. I buy bearings from Simply Bearings, you might find they have something.


Bikepete30/06/2021 19:01:20
242 forum posts
34 photos

Could you modify a lazy susan bearing maybe? Available big as you want, cheap as chips.... e.g.


Jeff Dayman30/06/2021 19:03:31
2234 forum posts
47 photos

If you have a boring head, you can put a single point tool in it and set it so the end of the tool describes the arc you need. You can then mount the boring head shank in a block on the tool post, rotating about the vertical axis, with close fit bearings so it can turn without chatter. Also make a clamp-on handle to turn the head and tool assy in the block to make your cuts in the turning stock in the lathe. Look up "ball turner based on boring head" to see this idea arranged horizontally, for turning the OD's of balls. For a groove, you arrange it vertically.

Another thought- if you have a mill and a spin index or rotary table - set up an endmill of the diameter of your groove, mount the work on the index or rotary table and rotate the work past the cutter. when finished, re-mount to the lathe and file and polish the groove to suit.

I also second the idea of going to a bearing factor first to see what it available. you may find an off the shelf bearing with the correct OD but ID too big, or vice versa, for relatively little money and of high quality. Then go to your lathe and make a spacer ring to take up the gap or gaps as needed to make the purchased brg fit your machine. The ring or rings can be retained by Loctite and or setscrews or by a shoulder machined on one side and a retaining ring on the other. The bearing firm can probably help you find a retaining ring if you need one.

duncan webster30/06/2021 19:04:52
4105 forum posts
66 photos

Would roller bearing do?

DC31k30/06/2021 19:08:07
725 forum posts
2 photos

SInce you mention 6mm dia. balls as a possibility, a standard RCMT06 insert would be a very cheap way to proceed.

John Haine30/06/2021 19:44:01
4712 forum posts
273 photos

What is the application? Will it run horizontally or vertically? How much loading? Depending on the answers different approaches may be possible.

Guy Thornhill30/06/2021 20:09:37
3 forum posts

There has been some great input here so thanks to all contributors. I'll cover a few of the points in one post.

1) I have a lazy Susan and unfortunately it runs quite a bit too rough and imprecise for my requirements.

2) I need a groove rather than a roller bearing in order to retain tightly one half of the assembly.

3) The insert options are really interesting however taking on board a few of the comments, I do have concerns over chatter. My lathe has reasonable power but would be considered of light construction.

4) I'll have a look at the design and see if a v groove is an option.

5) The 'ball turner' sounds very interesting but a lot of work. Given the tools I already have that could take me weeks.

6) I do have a mill but not a rotary table and I do like the idea of cutting the groove with the OD of an end mill. Also filing and polishing a first cut groove is definitely an option. As an alternative I am thinking about using a lollipop end mill like the link to get a groove from the end mill, then finish on the lathe. Is his a really bad idea?


7) The application has to run horizontal and is very light loading, say 10kg max. It is for a hobby prototype project and the compact element is key which means using and retaining a standard bearing will not be ideal.

Speedy Builder530/06/2021 20:11:07
2642 forum posts
217 photos

Braze a ball bearing onto a tool shank and then grind away half of the ball to leave you with a form cutter, but like Jason said, unless you have a "heavy" lathe, it will chatter. You may get away with removing most of the metal with smaller tools and clean up with a form tool. Make 3 tools the way I have explained, but grind one as a LH cutter and the other a RH cutter and the 3rd full form.

Neil Wyatt30/06/2021 20:14:40
19076 forum posts
736 photos
80 articles

A ball-nose endmill in a toolpost mounted spindle might provide a good enough finish?

Howard Lewis30/06/2021 20:16:12
6301 forum posts
15 photos

So far, no one has suggested grinding a piece of round HSS and mounting it a suitable holder .

It will certainly produce an external, or face, groove for a ball bearing; if the toolbit and ball sizes correspond.

Machining an internal groove may be a little more difficult, ,but should be possible with some ingenuity.

Obviously, being a form tool, speeds feeds and depth of cut should be minimal to reduce the risk of chatter.

Lubrication may help.

What do you think chaps?


JasonB30/06/2021 20:20:19
23022 forum posts
2763 photos
1 articles

Is an off the shelf 80 x 100 x 10 bearing going to be any thicker than you could make?

Flexing of the rings will also be a major issue if trying to hold in a 3 or 4 jaw chuck as they will easily distort

Ball nosed mill, ball cutter and endmill in the mill will all only do the inner race you you would need to do the outer in another way

Edited By JasonB on 30/06/2021 20:22:08

JasonB30/06/2021 20:24:07
23022 forum posts
2763 photos
1 articles

Howard, I think the OP covered grinding one

"I don't think I'll be able to grind anything nearly accurate enough with my grinding set up.

Howard Lewis30/06/2021 20:37:00
6301 forum posts
15 photos

If you take a piece of round HSS, of a suitable size, the only grinding needed is a rake angle on the end of the toolbit. Something akin to a diamond tangential turning tool, but with an oval end after grinding.

So no precision grinding, just an angle on the end, and a suitable holder to be made..

I used this method when needing a round track to use as an adjusting thread using a 1/8 ball bearing as the follower.

If accepted for publication, the method would appear in an article on a Shop Made Comparator..

It was merely a 4 mm pitch thread, 0.062" deep, with the Adjusting ring carrying two 1/8" balls, one on top of the other, to engage with the thread. Acceptable as an adjuster, but not executed well enough to be the track for a ball race, in this instance.


JasonB30/06/2021 20:45:40
23022 forum posts
2763 photos
1 articles

Assuming the round HSS needs to be held vertically in the lathe how would that work for the internal groove?

Rod Renshaw30/06/2021 20:58:00
376 forum posts
2 photos

As well as the usual pressed steel lazy susan bearings there are better quality ones based on two alloy rings with stainless steel ball bearings between, such as these below, from Amazon. I used one of these, and an old alloy pan, to make a rotating plier holder as seen on Steve's bench on "The Repair Shop", and it seems quite smooth and precise for such a purpose. I acknowledge the methods of cutting the grooves listed in the posts above but share Jason B's concern about the difficulty of holding a thin and possibly flexible ring without distorting it unless one has a 6 jaw chuck or other special equipment.

Lazy Susan Rotating Aluminium Metal Round Circular Turntable Bearing 140mm 5.5 inch Heavy Duty

Brand: Turners Quality Bearings

4.4 out of 5 stars 110 ratings


  • HIGH QUALITY: Heavy duty, corrosion resistant aluminium alloy
  • STRONG AND DURABLE: Full, stainless steel ball bearing race
  • EASY TO USE: Non-slip rubber feet for instant fit use
Ketan Swali30/06/2021 21:21:48
1431 forum posts
134 photos

Hi Guy,

Not sure if this helps..

Some of the thinnest -Slim section ball bearings similar to the inside diameter you seek or bigger can be found under the INA or Kaydon brands. See this link for examples. E.g. CSCA040, CSEC040 both of which have I.d. Of 101.6mm and o.d. Of 114.3mm or 120.65mm.

Ketan at ARC

Howard Lewis30/06/2021 22:06:33
6301 forum posts
15 photos

Answering Jason's question:

If the bore is large enough, the tool can be like a boring bar, with the toolbit held vertical, in a radial drilling in the bar, with the angle on the end of the toolbit providing the top rake. Being circular, the side clearances will be present. automatically..

Obviously not possible for a relatively large ball in a small outer race.

If you are sufficiently determined and inventive, most jobs can be done.


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