Rear tool post vs front tool post

[Merddyn’s DadParticipant @merddynsdad]

The two toolposts, front and rear, will be different due to the tool centre height and the tool size.

S

[Grindstone CowboyParticipant @grindstonecowboy]

+1 on what Steve says, at least as far as tool height goes. I can take some measurements of the standard Taig toolpost if you like, but it will be tomorrow.

Rob

[BazParticipant @baz89810]

Plus one for Martins comment, doesn’t matter where the tool is, front, back, above, below, it’s the confidence of the bloke turning the handle.

[Martin KyteParticipant @martinkyte99762]

Maybe, just Maybe the secret ingredient of the rear tool post is the confidence it will work.

(ps I do know that the geometry is favourable too)

🥴

[Simon MicklewrightParticipant @simonmicklewright48909]

Posted by Grindstone Cowboy on 22/03/2023 21:19:19:

+1 on what Steve says, at least as far as tool height goes. I can take some measurements of the standard Taig toolpost if you like, but it will be tomorrow.

Rob

That would be very useful but no rush.
many thanks.

[Martin KyteParticipant @martinkyte99762]

On a more serious note I wonder how many parting off issues in larger diameters are due to the use of 3 jaw chucks where the work moves in the chuck. ? The 4 jaw is far more stable for slicing off big diameters.
regards Martin

[not done it yetParticipant @notdoneityet]

Posted by Simon Micklewright on 22/03/2023 20:10:40:

Thanks Dave, yes as a newcomer to lathes and such accessories I am struggling to find the correct question. As time goes by and I read more the question does indeed change.

so the Taig tool post is the same as the rear tool post?

unfortunately the uk supplier does not have the front tool post in stock but does have the rear version.

they do look identical to my eyes.

Yet the price is different.

Simon,

You are learning quickly! Yes, your opening question was far too open-ended. Simplistic, even.

That you soon ‘admitted’ to the size of your lathe was a very necessary piece of the jigsaw.

Be careful with what you see on the ‘net. That pic, reproduced from a Taig advert(?), is absolute trash, if seen by a beginner and taken as normal. Taig would, no doubt, claim that neither of the cutters were near contact with the work piece, so nor would the centre support be necessary. Obvious to anyone with experience but to a complete newbie it may give the impression that tailstock support was not appliccable to that cutting scenario. 100% wrong, of course!

Light-weight lathes benefit from a rear parting tool. So do older middle-weight lathes which may have signs of wear developing. Solid/rigid larger lathes can cope better without (but might be better if wear is apparent). Truly commercial lathes were likely dumped/changed out if the wear was affecting the machine’s output/accuracy – and, of course, some of these have filtered down to the hobbyist.

Your lathe may be regarded as a ‘toy’ to those with huge industrial machines and large workpieces. For a clock maker, it is (maybe?) perfectly appropriate. Horses for courses’ and all that. Right down to those that simply say don’t try to part off with it. I would add that the material being cut might influence that choice.

My lathe was a good quality lathe, when new 50 years ago (cost about twice that of the local competition back then). I consider it to still be in good condition for its age but it does benefit by parting from the rear. For two basic reasons – first it is only a 5” centre height ‘hobby’ lathe and second, I’m just a hobbyist, not a ‘proper’ machinist.

Enjoy your Taig, if it is suitable for your needs. I suspect that later you may either change it for a larger machine or retain it and purchase another, larger, machine.🙂

[Nigel McBurney 1Participant @nigelmcburney1]

I have a rear tool post for my S7 its ok if making a batch of parts and a light tool eg a chamfer tool is needed to avoid tool changes on the front toolpost but I consider the cross slide though in proportion to the lathe is rather light in construction a distortion could occurr after a parting tool jam ,the thrust is up and cast iron is far stronger in compression than tension,so I never use the rear toolpost for parting off.

[egaParticipant @ega]

ISTR that Martin Cleeve used a steel cross slide on his ML7 special.

Edited By ega on 23/03/2023 10:11:24

[bernard towersParticipant @bernardtowers37738]

Taig toolpost dimensions are, front 1” sq and 1” from base to bottom. Of tool slot, tool slot 0.375” wide total height 1.750”. Rear toolpost is 1” sq, 1.236” from base to bottom of slot, 0.375” for slot withe total height of 2.00”. They also do a rear toolpost for parting off which is made from steel (the others from hard anodised aluminium) The parting version is much beefier and has the slot at an angle a la GHT and I find it works very well, I also use a small QCTP on one of my machines

[Alan JacksonParticipant @alanjackson47790]

With apologies for being flippant I wrote this some time ago

Alan

A while ago I tried out a vertical parting tool it worked ok but I must admit I did not give it exhaustive testing to destruction etc.

In order to clarify the operation of a vertical parting tool here is my rather primitive description of how I think it works.

Imagine that you are the parting tool holder whereby your two hands are held straight out from you body. You hands are gripped together and your fists are the cutting edge. You have a friend who represents the metal being cut and he (If you are a front parting tool) pushes down on your hands while you do you best to resist him pushing down. You can see that he can quite easily push your arms down. If you want to now become a rear parting tool you can turn round 180 degrees and your friend would now push your hands upwards still he can easily overcome your resistance to him pushing up. So in order to stiffen you up, say you are frozen solid or have rigor mortise and are wearing a large pair of lead diving boots to anchor you down. When your friend (or should I now say de-parting undertaker) pushes down on you hands he will not be able to move your arms down because they are rigidly fixed to your body and he have to apply more force until you tip forward on you toes. Note that as you tip forward you rotate about your toes moving your cutting tool hands deeper into the metal being cut. If you are now rotated 180 degrees to become a rear parting tool your friend (some friend) now has to apply more upward force until you tip backwards on your heels. Also note that your cutting tool hands now move away from the metal being cut as you rotate backwards on your heels. Now you have to play the part of a vertical parting tool as I am proposing, so you now can be thawed out or de- rigor mortised. So lay flat on your back and push one arm vertically upwards and clench your fist to form the cutting tool. Your friend now has to apply considerably more force to overcome your vertical arm. Your arm will be in direct compression and until your elbow or wrist give way you will have much less a problem resisting his downward cutting force. It will also not matter if you are a front or rear vertical parting tool as long as the rotating force is pushing down on your hands. You can now get up and go back to your work or whatever you were doing. I apologise for being so flippant but I hope it does explain the reasoning.

Regards

Alan

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 22/03/2023 19:26:15:

.

This may be an XY question! […]

So, we're all off with the fairies, debating Gibraltar tool-posts, parting off, and industrial techniques, whilst it looks suspiciously as if all Simon needs is a basic Taig fitting costing £7.80.

[…]

.

You have my nomination for ‘Post of the Week’ Dave

Succinct  … and it triggered some very helpful follow-up

MichaelG.

Edited By Michael Gilligan on 23/03/2023 11:14:55

[JAParticipant @ja]

Some of the photos posted seem to show the parting off tool mounted in the rear post with the cutting face upwards. In other words to part off the lathe would have to run backwards. I strongly believe a lathe, for any cutting, only rotates one way. I hope my observation is wrong.

I use a rear tool post on the Myford but have yet to do so on the little lathe. Watching the parting off bronze on the little lathe the build up of chips, trapped between the tool and the work, is alarmingly rapid. This leads me to believe a rear tool post works because it prevents this build up chips, just let gavity work.

JA

[Martin ConnellyParticipant @martinconnelly55370]

Sorry JA, clearly wrong. The lathe can be used either way if the chuck will not be unscrewed. So between centres, collets, bolted on chucks and D1 type mounted chucks can be used either way.

See this threading technique where the part is spun in reverse with an inverted tool to cut R/H threads with the tool moving away from the headstock.

Martin C

[Andrew JohnstonParticipant @andrewjohnston13878]

Posted by JA on 23/03/2023 11:35:45:

I strongly believe a lathe, for any cutting, only rotates one way.

Like this:

Lathe works equally well in both directions. To change direction just flick an electrical switch, no need to stop the spindle first.

Andrew

[SillyOldDufferModerator @sillyoldduffer]

Posted by JA on 23/03/2023 11:35:45:

Some of the photos posted seem to show the parting off tool mounted in the rear post with the cutting face upwards. In other words to part off the lathe would have to run backwards. I strongly believe a lathe, for any cutting, only rotates one way. I hope my observation is wrong.

…

JA

Nope, your observation is correct!

An advantage of Far Eastern lathes is their design is more modern than classic machines. Not entirely a good thing when applied to cut costs, but a good thing in that these machines can cut forwards or backwards equally well, almost. There are a few exceptions, such as when a DC motor is low-power reverse because it has staggered brushes, but my 3-phase lathe can spin its bolt-on chuck at full power either clockwise or anti-clockwise. And the power-traverse controls work in either direction too.

So I can part-off from the rear with an upside down cutter spinning anti-clockwise, or I can part-off with the cutter facing up with the chuck spinning clockwise. Gravity is alleged to  keep swarf out of the slot in the first set-up, but the saddle could lift. In the second way, spinning clockwise, the cutting forces can't lift the saddle, so the set-up is more rigid, a good thing!

I don't run clockwise all that often but it has value. The only real objection I can think of is carelessly taking a conventional cut on a lathe set for clockwise running, which won't work. But I'm self-taught and my understanding is full of odd gaps and misunderstandings. Is there another reason why I shouldn't run my lathe backwards?

Dave

 

 

 

 

Edited By SillyOldDuffer on 23/03/2023 13:09:26

[Grindstone CowboyParticipant @grindstonecowboy]

Bernard beat me to it, the only things I could add are the slot is 5/16" deep, and the grubscrews for holding the tool are centred on the slot and 1/4" in from each end. Central hole from top to bottom for long Allen head capscrew into a T-nut to hold it onto the saddle.

Rob

[egaParticipant @ega]

Posted by SillyOldDuffer on 23/03/2023 13:07:54:…

I don't run clockwise all that often but it has value. The only real objection I can think of is carelessly taking a

conventional cut on a lathe set for clockwise running, which won't work….

Unintentionally running in reverse can have damaging consequences. To guard against this when eg screwcutting away from the chuck I use a simple stop or gate on the forward reverse switch on my Willson lathe:

A poor photo; the stop is the shiny thing on the right hand switch; when not in use it lives on the left hand one from where it is readily available.

[Peter Cook 6Participant @petercook6]

To answer the original question about Taig Toolposts. The rear toolpost is different. This is a quick shot of three of mine.

Centre height from the cross slide is 31mm

On the right is a standard Taig Toolpost 45mm high, bottom of slot is 25mm from base. Top of 6mm Tool sits on centre height.

In the centre is a Taig Rear Toolpost with the tool mounted upside down. Overall height 51mm, bottom of slot is 31mm up from base – so inverted the tool sits on centre height.

On the left for completeness is a Taig rear mounting parting toolpost that uses a T shaped blade. The holder is inclined so that the blade can be set on centre height.

Hope this helps

The ones I use a lot get the handles as seen on the right. The less commonly used rely on the standard cap screw.

Sorry – didn't see Bernard's response!

Edited By Peter Cook 6 on 23/03/2023 14:37:33

[bernard towersParticipant @bernardtowers37738]

I like the idea of the resetable handles Peter.

[Peter Cook 6Participant @petercook6]

Bernard – idea stolen from Taig Micro Lathe Tool Posts, Boring Bars & Locking Levers (micro-machine-shop.com)

In the US you can buy 10-32 handles, but they are unobtanium over here. I use a length of 10-32 studding Loctited into M5 female handles which are easy to get (& cheap) from Ebay.

[Simon MicklewrightParticipant @simonmicklewright48909]

Thank you all again. Plenty to get my teeth into. Also thanks for carrying out the measurements and the photos of the Taig tool posts. Very useful.
The Taig I have acquired is missing many important parts but that’s a story for a new thread.

kind regards.

simon.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Simon Micklewright on 23/03/2023 16:58:54:

Thank you all again. Plenty to get my teeth into. Also thanks for carrying out the measurements and the photos of the Taig tool posts. Very useful.
The Taig I have acquired is missing many important parts but that’s a story for a new thread.

kind regards.

simon.

Photos are always helpful if you can manage them. Not obvious how to do it, so the instructions are here. At least the Taig is still in production – not as hard to get spares for as a 1911 Relm!

Looking forward to your next lathe problem – it's always good to get machines working again.

Dave

[old martParticipant @oldmart]

I'm sure it will have been mentioned, but with a screw threaded spindle type of lathe, it is only safe to use a rear toolpost with inverted cutters unless you can be sure to lock the chuck to the spindle. Collets in the spindle would be ok as they are much less likely to unscrew. I made a rear toolpost which can hold industrial parting off blades inverted, and added a rear saddle lock to maximise the stiffness.

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