Tool post project

A quick change tool post has been on my to buy or to do list for far too long now. Having researched a fair bit on the subject I narrowed the options, so if I were to buy a ready made one I would go for the Aloris wedge type tool post. On the other hand building my own is more difficult to decide which way to go - I was originally in favour of the Norman type post, then I saw Mikes's modified Norman post with expanding collet which I liked even better. Then somewhere on the forum I saw mention of a Pratt Burnerd tool post - I'm basing my build on the latter.

The tool post will fit on a WM280 lathe, I plan to replace the top slide with a solid block later on, but I want to tool post to be interchangeable with both top slide and solid tool post mount. The tooling I use is mostly carbide insert type and I have recently acquired a lot of 16mm shank lathe tools, so the holders have to fit these tools.

This is the general layout of the tool post as compared to the 4 way tool post (next to it) A brief description of how it works: The cutting tool is held in a tool holder clamped by 4 grub screws (not visible). The tool holder is clamped to the surface of the topslide by means of a top plate. The two round pins concentrate the clamping force downwards and at the same time prevent the tool holder from sliding under cutting forces (hopefully).

Under the top handle nut will be a spherical washer set to take into account any misalignment so that the tightening force rest squarely on the top plate.

Exploded view of the tool post. The central stud is 22mm diameter at the base, this is a direct fit to the top slide without any modifications. The top portion of the pin is threaded with a 16mm diameter - not sure of the pitch I'll use for now.

The tool holder adjustment is not done like the Aloris, Dickson, Norman with set screws. Actually there's no adjustment as the tool holder will be machined to the correct center height straight away. As the tooling is insert tooling the center should be always the same for that particular tool in it's holder.

I think overall, it's pretty simple to build, and should be similar to the 4 way tool post in rigidity. As for materials to build it from, I'm sot sure. The 2 locating pins will 10mm be silver steel rods, the rest I might use some tool steel ( or maybe I'll start of with mild steel to make life easier!)

Any thoughts regarding the design and if there's some major flaw which I did not consider?

Chris

Think I would have some way to index the in/out position of the holder so that if you were doing a batch of items that needed a tool change you could swap holders and be able to use the same handwheel settings rather than have to measure each time a tool is holder is changed. Would also stop the holder being pushed back towards you.

Maybe move the half round groove towards the middle so you have more thread depth for the grub screws

Interesting, especially since I currently making a tool system for my little WM180....

Presumably, when the centre post is released so are th two rods..(?)...this could be inconvenient

Also, what is the arrangement for adjusting tool height?

Lastly, what if any, ar the advantages over the 'plain and simple' Norton design?

Posted by ChrisB on 28/08/2019 18:20:51:

The tool holder adjustment is not done like the Aloris, Dickson, Norman with set screws. Actually there's no adjustment as the tool holder will be machined to the correct center height straight away. As the tooling is insert tooling the center should be always the same for that particular tool in it's holder.

Hi Bob, well spotted, the rods can either be spot welded to the top plate or with adhesive. It makes no sense having them running around.

With regards to tool height adjustment, as I mentioned in my original post, I will be using insert tooling. My plan is to make a batch of holders to a standard size, and then machine the bottom surface to obtain the center height for that particular tool. As it's insert tooling once the height is set (by machining the bottom face of the holder) there is no need for further adjustments in the future. This will obviously not work for HSS tooling.

Not sure what the Norton design is, but if you're refering to the Norman tool post, the tool holders are quite large compared to this, less material required, less machining required, and I think this may be more rigid.

Posted by JasonB on 28/08/2019 18:39:59:

Think I would have some way to index the in/out position of the holder so that if you were doing a batch of items that needed a tool change you could swap holders and be able to use the same handwheel settings rather than have to measure each time a tool is holder is changed. Would also stop the holder being pushed back towards you.

Maybe move the half round groove towards the middle so you have more thread depth for the grub screws

Good points Jason, Hadn't thought about indexing the holder, but that's easy fix, can be done. Regarding the round groove, I'm afraid that moving the groove further towards the center of the tool post will make the grip on the holder less effective. I could increase the thickness of the tool holder tho so Icould use longer grub screws. As is the screws are currently M8 x 6mm

The advantage is that the tool cartridge is tight onto the topslide and gives ridgidity.I made a toolholder which is in my album which is based on the Pratt burnerd holder.Mine, one has to pack the tool in it's holder to centre height but once done your there and unlike this design the holder can be removed and replaced as before and cannot move in the toolpost.I like the toolpost Chris.

Frank

The four pins won’t all press onto the tool unless the rod deforms substantially. Also I think a key and key way would locate the holder, the key can be a flatted pin.

Rather than use two pins why not make the top with two angled faces one acting on the holder and the other on the main body. This will pull the tool holder into the body.

It looks good because it keeps the cutter closer to the centre of the carriage with no tool holder hanging out the side!

Probably not quite as convenient - I would expect you to need the odd shim for perfect centre height adjustment, but a definite improvement over a non-QCTP.

Frank’s rear pin, for positioning, looks good.

The long-travel on my lathe is far too ‘coarse’ for intricate manual feeding - is yours well geared down?

Hi Frank, I've seen your photo album, fine set up! The principle is very similar, how do you like the rigidity of this tool post?

In this design, the tool holder slides forward or backwards when the top nut is loosened, so you can replace with the next tool easily. I thought I'll do away with shimming so I will machine the tool holder to centre height instead.

Hi Howardt, those four pins should be grub screws which in turn clamp the tool to the tool holder. The grub screws will sit lower than the round groove in the holder so the two rods will not be touching the screws.

Making a V-groove may be a good idea, it will introduce some extra setting up to do it but will do away with those rods...food for thought, thanks!

Taking your design to extremes, assuming all your tools are the same size, would be to put the round groove directly in the top of each tool. It could be done with solid carbide bullnose cutters, although the ends wouldn't stay sharp very long.

So I took some of the suggestions and replaced the round rods with a sort of a V - groove (a half V to be precise). Added an indexing wing at the forward end of the tool holder such that the tool will always go to the same depth. And increased the tool holder height so now I can use m8 x 10mm grub screws. Are M8 excessive? Would M6 be more suitable? Off hand cannot remember what's installed on the 4 way tool post!

Here's tool post version 2

Tool holder with beveled edge instead of the round groove. Theory is when tightening the top plate the holder should press down and in against the tool post and top slide. The extended part at the forward of the tool holder is the indexing part which will mate against the tool post. Grub screws should not extend beyond the bevel.

I have a feeling that different styles e.g. aluminium type tips against steel tips have a different tool height you would need a different tool for different tips. and different manufactures don't guarantee a fixed height with another manufacturer.

David

Hi Chris ,A dowel pin in the side of the tool post with a locating hole in the tool cartridge would solve the repeatability and the location issue.I have a dixon type tool post and I find that my design is quicker and uncluttered on the top and this type of holder is more ridgid.

Frank

The proposed designs will not restrict the 6 degrees of freedom of the toolholder. You would be wise to do a Google search about restricting the 6 degrees of freedom of any element in a tooling system you do not want to move relative to anything else, and repeatably locate to other things. These things are fundamental to any toolholder, yet many for sale on the market , and many shown in ME and MEW do not achieve it.

Your latest design has a further issue in that the setscrew thread engagement is short, and after some use the top of the thread will likely bulge out into the angled clamping face.

Hi Chris you don't have to have an angle on the rear of the clamp you only need a step and shoulder to bear against which would be simpler to machine and more stable. You don't need such a large angle on the front side of the clamp which would give more thread length to tool clamp grub screws and then you could lessen the amount you unscrew to remove the toolholder in close proximity with job.

David

Edited By David George 1 on 29/08/2019 07:08:01

But in what way is it lacking? The only one I can see is non-repeatability of rotation about the clamping stud. In all other directions it seems OK (if one agrees that it does not need to be restrained from pulling into the workpiece).

To the OP, it may be worth thinking a little of the QC aspect of the design. Right now, to change a tool fast, it has to go towards the centreline of the lathe. This means winding the carriage back past the end of the work or winding the cross slide back to give clearance. If you need to remove the tool (perhaps to measure something) without altering your settings, this may annoy you.

My plan is to machine the bottom off the holder to the correct centre height and as I'll be using insert tooling no further adjustment should be required - hopefully!

I saw that but doubt you will achieve perfect facing (no trace of a nipple) without a great deal of hassle. Shimming seems so much more convenient than milling off tiny cuts, taking care not to go beyond the perfect size and effectively ‘scrapping’ that tool holder for that cutter!

It is coarse as you say, but still manage manual feeding - very carefully. The top slide is much better for creeping up to the size.

I had noted you mentioning doing away with the top slide at some point? Won’t that make it imperative to use the long travel for all intricate turning operations? I was just thinking ahead for you!

Thoughts...

• No height adjustment.
• Those grub screws will have very little thread engagement and not be long enough to allow for different size tool shanks.
• Unclamping will lose toolpost location.

Sorry to be negative...

Here's an alternative idea, if you don't need height adjustment - why not do away with toolholders, just provide a place for the tool to sit and clamp directly on top of the tool shank?

Basically this with a cam instead of screws?

Neil

Sorry for the hijack, but I thought I'd share this idea for a quick and dirty toolpost. I've already thought of a couple of refinements.

The main limitation is that tools will need shimming.

Might actually make one of these. Without the step (tool actually resting on the topslide as originally intended) it would be ideal for the Sooper Dooper Adept.

Neil