Tangential Tool Holder

In a recent update to an ongoing thread (Lathe Improvements?), Niels Abildgaard included a photo of a machining setup which featured a short, stubby tangential toolholder which barely overhung the edge of the topslide - The design commended itself to me as a Hobbymat owner, as I've always regarded the standard toolholding provision to be, well, less than perfect, perhaps.. The Hobbymat does not respond well to excessive or uneven loads applied to the surface of the topslide, and the tools must be shimmed to centre height - the opportunity to try and alleviate some of these admittedly minor annoyances and to be able to employ a simple and easily set tool for the most commonly undertaken, facing and turning tasks seemed to be worth an experiment.

I quite shamelessly set out to produce a smaller but more-or-less identical version of this toolholder with the aim of trialling it, guessing at the angles (12 degrees for toolbit and back rake, 85 included at the nose) from extra photo's that Niels kindly posted.

The initial results are promising - the holder was relatively simple to make, cuts well (when arranged not to rub - see below) and sits firmly on the topslide without having to apply brutal levels of torque to the clamp. It's currently fitted with a 2mm round HSS toolbit.

The tool as it currently exists is very much a "first-off" and I throw it out here, naked in it's imperfections, for scrutiny or comment by anyone interested.

I'd welcome opinion on whether the 12 degree toolbit angle is in the right ballpark or whether it could usefully be increased to provide more clearance without increasing the risk of weakening the edge - and will I need to change it if I wished to use carbide?

There is a "To Do" list - I clearly need to reduce the height of the upper face/front chamfer to avoid the nose rubbing, reduce the included angle of the nose to provide more side clearance, and experiment with tool-grinding angles to find the optimum balance between cutting angle and edge-strength. And I may move the clamp screw rearward just a little..

Any comments and suggestions will be gratefully received

Edited By DiogenesII on 06/06/2020 19:55:27

Make the Mk2 with a 45 degree slope and see if it is any better or worse. It would be possible to use the other end of the existing tool and remove the unused cutter, or even use the other end of the cutter. I am always thinking of ways to reduce overhang on a much bigger, heavier lathe. Should you wish to try carbide, small diameter blanks are easy to get on ebay. To cut them, you need to score around the diameter with a diamond file, put the carbide in soft jaws in a vice and snap of at the score. It quite often breaks just where you want it to. Wrap the end you are holding in some rag just in case it shatters.

Edited By old mart on 06/06/2020 20:11:35

There have been at least two Tangential tool holders published in the past few years, so you are in good company, and you now have a most useful turning tool.

One involves milling a slot in the holder at 12 degrees for the square toolbit, whilst the holder is inclined at 12 degrees also. It bis easy to get the compound angle set up wrong!

I have made two versions, one for 1/8 square toolbits and another for 5/16 square..

The easier one to make involves milling the slot for the toolbit at 12 degrees, and then milling the shank of the holder so that upper and lower surfaces are at 12 degrees to the sides of the holder.

To sharpen the toolbit. it is held with the corners vertical, on a jig which inclines the toolbit at 20 degrees, in one case, and 30 degrees in the other.

The commercial version uses a similar jig to hold the toolbit for grinding.

All the above allow the one tool to be used for sliding or facing cuts without altering the tool setting.

A necessary accessory has to be a centre height gauge, to facilitate setting the cutting edge to centre height.

Howard

Hi, thanks old mart, I hadn't considered making it a double ended, but that's a logical plan for a test bed.. It'll also be convenient 'cos as you can see in the second photo, it was the last end of the bar..

It is my plan to make a tangential holder for 3mm round carbide that suits my 250 lathe..

It was once measured by a Boing 737 (old model) captain that I could decide to stop,remove toolholder ,regrind.put back on lathe and start cutting again in less than two minutes.

This is somehow due to having upper surface of holder exactly on lathe centerline when underside sits firmly on compound slide.

It has been nessecary to measure that precisely and I did it this morning

I did it by turning a scrap piece of alu so that it could go over compound slide.

A toolbit and a feeler gauge of 4.08mm could just pass under the 39.68mm round.

39.68 divided by 2 is 19.84mm plus the stack of 4.08 mm gives a centerheigth of 23.92mm over compound slide surface.

The he next turning was made 47.84mm and a single layer of kitchen alu foil can go between.Two certainly not.

Foil is very close to 0.01mm.

My centerline is 23.93 or 4 mm over compound slide.

Edited By Niels Abildgaard on 06/06/2020 20:50:33

Interleaving text and photos is not easy.How do I put a phto from album some text a new photo etc?

Edited By Niels Abildgaard on 06/06/2020 20:56:26

The next picture shows that deciding distance from clamp stud to cutting point is not trivial and length of virgin toolbit is not either.

I have broken more than two turning compound slide back.

Edited By Niels Abildgaard on 06/06/2020 21:03:10

Manufacture can now start and I like to do it in the fourjaw and using most modern rocket science angle measuring equipment to get 12 degree toolbit angle.When i took the last picture I had to realise it was a scrapper.The future toolbithole was 3 mm from centerplane.Old men shall not calculate in head anymore.

Will start a new tomorrow.

Many thanks, both;

Howard - your information is a useful reality check, and confirms my thoughts on the necessary angles - the toolbit is ground at c. 24 degrees and inclined at 12, so I feel some reassurance there. For the current "testing of the principle", I've been using a "clog-heel" type clamp so that I can quickly swing the tool between the necessary orientations required for "turning" and "facing" - I do recall the "inclined-base" version, and will refresh my memory again, thank you for the prompt. I agree regarding the utility of a centre-height gauge, which I already have, and indeed, dovetails neatly into the observations of...

Niels - very canny, the holder will be going under the mill tomorrow and will emerge 2.2mm or so thinner along it's back.. I will not have to fish in oily swarf for the tiny hex key ever again..

Are you able to both side & face with it in one position? .."sharpening" the angle of the nose, without thinning down the clamp "jaws" is becoming the most head-scratchingest part of the job.

I'd like to see more of your build if possible..

I have been wondering if making a holder for 1/8 inch round toolbits would allow an even better finish to be produced.

Presumably, to minimis the risk of chatter, the fishing cut would need to be small.

The other problem would seem to be ensuring that a round bit is presented to the work with the cutting edge at the correct angle.

Looks like yet another job on the Roundtuit, after the present three live projects have been completed. There are also three more in very long term hibernation!

Howard

When I made my tangential holders I used 12* for side clearance and end clearance for a 1/4" bit. After seeing the quality of finish produced by the round bit I will be making a tsngential holder for a round bit.

Good morning

A picture showing combat area from below and one showing going in a 90 degree corner.The angle between the cheecks can be 90 degree of course,but is difficult to set by eye.Have tried 85 degree but prefer 80 to day.

Machining of cheecks is last operation as it has to be done reasonably controlled relative to toolbit.

This has shown me that carbide can cut carbide.

I am impressed by Pauls tantool with a 2mm round toolbit.

How is the flexibility slit cut?I have tried with a hacksaw and was not impressed.

Edited By Niels Abildgaard on 07/06/2020 06:41:44

Good morning

For my own part, I have experimented with round tool-bits in the past, and have found 3mm or 1/8" is probably about the useful limit on the small machines I have (I have a tired ML7 as well) if chatter is to be avoided.

Niels, to cut the slot takes a keen eye, and a steady hand - and a .050" slitting saw - I considered hand sawing, but like you, I find it leaves a finish that is not good for public viewing. No-one will ever see pictures of my mandrel handle!

Hello DiogenesII

The way to machine the cheeks can be seen here

Old pictures

I have never been very at ease with slitting saws and You just use one a little more than a mm thick?

What is Your centerline distance from compound slide top?

Edited By Niels Abildgaard on 07/06/2020 09:20:26

Ha, I am being overtaken by posting events! Niels, to respond to your old post - it is gratifying to see that your CAD images are more or less identical to the holder as I have it - I made the nose angle 85 degree, but will make it narrower on the next one. I have filed it for easement and now need to experiment to see how tightly I can approach from the side.

Howard, I find that the 2mm bit (as I currently have it ground and held) is limited to a useable cutting depth up to about 0.25 mm - adequate for the Hobbymat, but I think there are probably better choices for bulk stock removal - it is possible Niels can achieve better, not least because he has spent far longer in refining his design, and has a more solid platform from which to work.

It strikes me that CAD may hold the definitive answers on cutting depth, which will surely be tied to the logical mathematics of an acutely-sectioned cylinder?

As to setting, in practice, I find that because the cutting edge is plane and somewhat reflective that orientation is easily established by eye and intuition, although being plane, it ought to of course respond to the attentions of a small but easily constructed setting jig.. Another thing to get round to!

Slitting saws - I think I must have started to use them whilst I was unaware of the dangers, and so they do not cause me any concern - use a speed at the lower end of the required m/m, feed by hand gently until the teeth are fully engaged in the slot and thern you can up the feed rate just a little to keep it cutting cleanly - maybe you know that "hissing" kind of noise when steel is cutting nicely - like that, and like all sawing, best results by not pushing too hard, just each tooth cutting off a nice chip.

For a small job, I'd rather go slow and not use oil, than use oil and have the chips turn to a sticky mush in the slot, better to keep them free to exit. Never use CT90!

The centre height is about 10.5 above the slide, but accurately measuring is first job of the morning!

Sincere thanks for your advice so far

Another approach here.

And for calculating the grinding angles.

I once made a set of holders for a Myford that has only about 16mm from base to center and they looked wrong.

The mentioned 737 captain proposed a sligth change and it looking something like this.

The grinding of the carbide top is not difficult.

Make it more or less horinzontal and it works very well

I tried 5 degree downward and that worked but 10 degree neative did not.

Edited By Niels Abildgaard on 07/06/2020 09:36:04

Edited By Niels Abildgaard on 07/06/2020 09:38:35

Enviably logical! ..I wish I had that clarity of vision in the workshop.. A job for this afternoon..

Concerning angles of tangential grinding.

As said for round toolbits horizontal flat is as good as anything else and does not dig in in brass or some of the nastier bronces.

For square toolbits it is another case.

If You lean it 15 degree in as the Australian Diamond Tool and grind top horizontal there will be around 89 degrees between the two cutting edges and this is next to impossible to adjust with old mens eyes if you want cutting and facing with same toolsetting.To ease it toolbit is ground in a rather obscene angle with a jig,but this makes cutting tip less robust.

For my 2 and 3 mm square carbide sticks I did it otherwise.I bougth a swing grinder from Swindon and modified one face so that the cutting corner was 85degree and that was enough for my brain and eyes at that time.Today I wish it had been 80 degree and I have at least twenty modified 2 times 2 (almost) 60mm long and that will last me out.

Concerning round tangential toolbits.

It was tried with 3,4 and 6mm round carbide and flat top on mild steel.

It worked very well until depth of cut was equal to radius of toolbit ,that is 1.5 and 2 and 3mm.

The cutting edge was much more robust than any of my homebrewed square things.

Interupted cuts,cast iron skin etc

For our small lathes there is no reason to opt for bigger toolbits as 1 to 2mm depth of cut is power limit anyway