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Profiling tools

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Robin Graham20/08/2019 00:36:57
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I was looking at designs of radius turning tools based on boring heads and came across this video. The author (Ade Swash) uses an RCMT 06 carbide profile insert at the business end of the the tool, and it looks like it works well. He also uses the same insert for cutting the relief in the stock for his ball turning demo.

Hmm I thought, I've got one of those 6mm diameter profile tools (bought when I had only a tiny lathe which couldn't cope with it), maybe it'll work with the bigger machine I have now. It did, once I'd conquered nerves and was assertive with the cross slide, like you have to do with parting.

Question is - how big a profiling tool can one run on a 'domestic' lathe? I had a look at JB and they list up to 25mm diameter which would be 75mm (pi=3) cutting engagement if plunged to radius. Surely that would need a very big machine? Even 12mm would speed things up for me though if possible.

I have a 12x36 lathe and I'm working in brass.

Robin.

John Reese20/08/2019 02:23:17
782 forum posts

As the width of tool engagement increases you will begin to get chatter. Screw machines could run very wide form tools, Most hobby lathes aren't sufficiently rigid to handle wide contact without chatter.

The ball tool forces are primarily into the cross slide feed screw. Increased load on the tool will tend to decrease the depth of cut. With a form tool n the toolpost the cutting forces tend to tilt the tool down and to the left, momentarily increasing the depth of cut. That is when chatter begins.

JasonB20/08/2019 07:06:07
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A lot will also depend on material both type and diameter. Brass cuts easily but if too slender the cutting tool will deflect it and more chance of chatter. Stick out can also be an issue when clearance for the ball turner means the work is a long way out of the chuck.

Your 75mm figure would be if the whole insert were touching, at the most only half will be in contact so 37.5mm and even then as you get further around the tool the depth of cut lessens to nothing.

This form tool probably had a contact length of 30mm on my 280, stock is 16mm square

Biggest issue using a round insert as shown in teh video is the large fillet you are left with where the ball joins the stock which becomes proportionally greater as ball diameter decreases and the wide cutting action of the "blunt" round tip will put more load on the work needing a larger dia contact with the parent stock, an RCGT rather than a RCMT would help a bit as the edge is sharper as would going down to a 5mm dia insert to reduce fillet dia and contact length.

 

Edited By JasonB on 20/08/2019 07:26:24

Michael Gilligan20/08/2019 07:32:42
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Posted by JasonB on 20/08/2019 07:06:07:
.
an RCGT rather than a RCMT would help a bit as the edge is sharper.

.

A quick question if I may, Jason

I fancy trying the RCGT 06 inserts and found these: **LINK**

https://www.rdgtools.co.uk/acatalog/RCGT-06-CARBIDE-TIPS---INSERTS---5PCS-76658.html

The box is clearly labelled QTY 10 ... but they are selling 5

Am I missing something [maybe five inserts] ? ... or is that the appropriate unit price ?

MichaelG.

JasonB20/08/2019 07:51:44
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Does say "box of 5" and around £4 a go would be right for reasonable quality. You could also try APT who will sell you a box with just two inserts of a slightly better quality.

Can't say that I use my one of these cutters very much but do use grooving & profiling type with the 2mm dia end more.

Vic20/08/2019 08:23:03
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There is a guy on eBay selling the 6mm polished cutters. Winning bids are normally around the £30 to £35 mark. This though is for three boxes of Ten inserts. I’ve now got a good supply of them. I bought them for use on wood turning tools for hollowing but I also have a profile tool for my metal working lathe. I also recently made a flycutter for my milling machine that takes these cutters.

Michael Gilligan20/08/2019 08:40:58
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Posted by JasonB on 20/08/2019 07:51:44:

Does say "box of 5" and around £4 a go would be right for reasonable quality. You could also try APT who will sell you a box with just two inserts of a slightly better quality.

Can't say that I use my one of these cutters very much but do use grooving & profiling type with the 2mm dia end more.

.

Perfectly aware that it says "box of 5" Jason ... hence my question.

Thanks for the confirmation regarding unit price ... That's what I needed to know.

MichaelG.

Michael Gilligan20/08/2019 08:44:14
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Posted by Vic on 20/08/2019 08:23:03:

There is a guy on eBay selling the 6mm polished cutters. [ ... ]

.

Thanks for that, Vic yes

MichaelG.

not done it yet20/08/2019 10:00:31
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Posted by Robin Graham on 20/08/2019 00:36:57:

I Question is - how big a profiling tool can one run on a 'domestic' lathe? I had a look at JB and they list up to 25mm diameter which would be 75mm (pi=3) cutting engagement if plunged to radius.

Robin.

How are you calculating that value? Circumference is Pi.D. Cutting a full half circle would be Pi. D/2?

Neil Wyatt20/08/2019 15:09:51
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I think the 'profiling' inserts are circular ones intended for use with CNC or templates (because it's easiest to calculate the offset with a circular cutting edge). They aren't designed to be 'plunged' although within reason you can use them this way to cut a concave surface or filleted inside corner.

Neil

Robin Graham20/08/2019 21:29:22
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Posted by not done it yet on 20/08/2019 10:00:31:
Posted by Robin Graham on 20/08/2019 00:36:57:

I Question is - how big a profiling tool can one run on a 'domestic' lathe? I had a look at JB and they list up to 25mm diameter which would be 75mm (pi=3) cutting engagement if plunged to radius.

Robin.

How are you calculating that value? Circumference is Pi.D. Cutting a full half circle would be Pi. D/2?

Badly blush . I should have said Pi=6 obviously*. You are right of course!

Thanks for discussion, and in particular for Jason's pic - it may be that I'd be better off making custom cutters from silver steel or gauge plate for ornamental work in brass. If that can be done with a 280 I have no excuse for not doing similar with a slightly heavier machine.

I'd actually ordered a couple of RCGT inserts from JB cutting tools anyway - I've been surprised how well GT type inserts work with brass, despite having quite an aggressive positive rake. They seem to work well for finishing cuts in mild steel as well.

Robin.

*There's no fundamental reason why Pi shouldn't equal 6, it just needs confidence and a  determination to make it happen. Apologies if that breaches forum rules.

R.

Edited By Robin Graham on 20/08/2019 21:32:01

Edited By Robin Graham on 20/08/2019 21:37:29

Edited By Robin Graham on 20/08/2019 21:42:33

Andrew Johnston20/08/2019 22:14:18
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Posted by Neil Wyatt on 20/08/2019 15:09:51:

I think the 'profiling' inserts are circular ones intended for use with CNC or templates.........

Correct, like this:

conrod_3.jpg

The sheet steel template and follower can be seen bottom right. Given that the follower needs to be the same shape as the tool bit it is simple to make a follower for a circular tool.

Andrew

peak420/08/2019 23:20:42
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Posted by Vic on 20/08/2019 08:23:03:

There is a guy on eBay selling the 6mm polished cutters. Winning bids are normally around the £30 to £35 mark. This though is for three boxes of Ten inserts. I’ve now got a good supply of them. I bought them for use on wood turning tools for hollowing but I also have a profile tool for my metal working lathe. I also recently made a flycutter for my milling machine that takes these cutters.

Any chance of a link, or sellers name/profile please.
My ebay search fu seems to be failing.

Thanks Bill

Michael Gilligan20/08/2019 23:36:13
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Posted by peak4 on 20/08/2019 23:20:42:

Any chance of a link, or sellers name/profile please.
My ebay search fu seems to be failing.

Thanks Bill

.

Mine worked O.K. this morning , Bill

Following Vic's clues, I found this: **LINK**

https://www.ebay.co.uk/itm/NEW-30-CERATIZIT-TURNING-FACING-GROOVING-RCGT-0602-BUTTON-FACING-MILLING-INSERTS/123875882730

MichaelG.

.

Assuming you win ... do you need 30 ?

Edited By Michael Gilligan on 20/08/2019 23:37:46

peak421/08/2019 00:14:28
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Posted by Michael Gilligan on 20/08/2019 23:36:13:

Assuming you win ... do you need 30 ?

Edited By Michael Gilligan on 20/08/2019 23:37:46

Probably not, why would you be after half a batch; I'm currently watching.
They're not something I've really used, but a holder for these came with my used GH1330 when it arrived. There's one in it, but I've been keeping an eye out for cheapish spares, as the one I've got is probably past its best.

Bill

Michael Gilligan21/08/2019 00:41:45
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P.M. sent, Bill

MichaelG.

SillyOldDuffer21/08/2019 08:56:56
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Posted by Robin Graham on 20/08/2019 00:36:57:.

...

Question is - how big a profiling tool can one run on a 'domestic' lathe? ...

I have a 12x36 lathe and I'm working in brass.

Robin.

 

 

 

Looking at it another way, what would stop a domestic lathe using wide form cutters?

  • The ultimate limit is the power of the lathe's motor. How much energy is needed to cut a particular metal is determined by the metal's tensile strength, and, although brass is weaker than steel, the difference in tensile strength isn't massive. Therefore the rule of thumb 1HP will remove one cubic inch of steel per minute can be used as a guide to guestimate the HP needed to achieve a particular depth of cut and feed-rate. The minimum power motor needed to drive a form-tool can be calculated from the minimum feed-rate needed to take a satisfactory cut along the edge, say 0.001", while the maximum theoretical feed rate would be the one where the motor is just powerful enough to meet the demand. (You can't remove more than a cubic inch per horse power per minute).
  • BUT a second limit will be more important on a hobby machine. The amount of power that can be put into a cut depends on the machines ability to absorb the forces involved without vibrating or distorting. With heavy cuts the tool and tool-post are the first features likely to bend, but the saddle and other parts can move as well. A heavy industrial lathe will do better than a hobby machine because it's more rigid.
  • Other issues are the shape of the form and the strength of the work-piece. A form shape that clears swarf naturally will do better than one that tends to trap it, as parting tools do. And a thin or poorly supported work-piece might bend away from the cutting edge, or break.

In practice a hobby lathe should work reasonably well with larger form tools than might be expected especially if light cuts only are taken. I'd experiment to find out the maximum a particular lathe can do because so much depends on the machine and how fast you need to work. To find the limits start small and move up in stages. As an index Jason's encouraging example shows what can be done on a WM280, a lathe heavier and more powerful than a Super7, but smaller than a Boxford. Form tools on a mini-lathe would be more restricted, but scaled to suit they should still be usable.

Dave

Edited By SillyOldDuffer on 21/08/2019 09:03:09

Michael Gilligan21/08/2019 09:13:08
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If I may just add a little to Dave's analysis: An appropriately located 'Gibraltar style' tool post should optimise the lathe's ability to use form-tools.

Whatever its other merits; the ball-turning device in the video is a fine example of how not to mount a tool if you want to reduce chatter.

MichaelG.

Vic21/08/2019 12:26:30
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Posted by peak4 on 20/08/2019 23:20:42:
Posted by Vic on 20/08/2019 08:23:03:

There is a guy on eBay selling the 6mm polished cutters. Winning bids are normally around the £30 to £35 mark. This though is for three boxes of Ten inserts. I’ve now got a good supply of them. I bought them for use on wood turning tools for hollowing but I also have a profile tool for my metal working lathe. I also recently made a flycutter for my milling machine that takes these cutters.

Any chance of a link, or sellers name/profile please.
My ebay search fu seems to be failing.

Thanks Bill

Here you go Bill.

**LINK**

I know a couple of people that have got these and the winning bid is as said normally around around the £30 - £35 mark which is obviously a very good deal for 30 inserts.

Robin Graham22/08/2019 23:15:16
582 forum posts
129 photos

Thanks for further discussion, Dave (SoD), yes, I know about the cubic inch per minute per HP thing but I think your second limit is the rate determining factor - in my case at least. My lathe has a 2HP (on the plate - input or output not specified) motor but I'm pretty sure it wouldn't be up to taking 2 in^3 per min! Obviously there are a lot of other variables as you say. I shall experiment!

Michael - I had the same misgivings about the way the device was mounted. I'd not heard of Gibraltar toolposts (why Gibraltar? Rock solid?) but my plan was essentially the same - a solid post mounted on the cross slide. I rarely need the additional degree of freedom given by the top slide - it mostly just gets in the way, so I'll be going along those lines.

Thanks also for links to cheapo cutters! Ebay came up with 'you might also be interested in... Ten CCMT inserts for 3.99

Rude not to! Especially as I get a 24p discount. For some reason.

Robin

Edited By Robin Graham on 22/08/2019 23:18:09

Edited By Robin Graham on 22/08/2019 23:18:25

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