Tool post project

[ChrisBParticipant @chrisb35596]

Did some further modifications and now I think I have the final design for the tool post. Next is materials to make it from – what are the recommendations?

My plan is to use mild steel for all parts apart from the central threaded stud and top plate. The stud I was going to make it from recycled 8.8ht bolt.

My main concern is the tool post top plate as it will carry most of the load, so I'm not sure if mild steel will be up to the job.

[ChrisBParticipant @chrisb35596]

After some online searching regarding what steel to use I think I'm going for EN24T for the top plate. For the tool post block I may go with cast iron – if it does not machine well I'll go with EN24 as well. Tool holders black mild steel. For the solid tool post mount it's cast iron.

Could not find any 80mm square section material locally, so I'm going to have to get round stock and figure out how to cut it. My bandsaw can cut max 105mm round but to fit 80mm square in a round I will need 120mm round bar – not sure if the bandsaw can cut that…

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ChrisB on 30/08/2019 21:34:03:

[ … ]

My main concern is the tool post top plate as it will carry most of the load, so I'm not sure if mild steel will be up to the job.

.

I'm coming in to this very late, Chris … but may I suggest that you look around for a forging that might be adapted to serve as your top plate.

I can't think of anything specific at the moment, but: It has the general look of something that might be used with steel beams, or perhaps in an Automotive application.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

PostScript:

The plate in this clamp is probably not ideal … but I think it's indicative of reasonably priced forgings being availabe:

**LINK**

https://www.scaffolding-direct.co.uk/scaffolding-clamps-48-3mm-drop-forged-band-and-plate-10-.aspx

MichaelG.

[JasonBModerator @jasonb]

I would have thought the 3mm or so of the scaffold fitting would flex more than the 6mm or so that it looks like Chris has drawn as the thickness of his top clamp.

If you want to save cutting metal then an offcut of 76 x 38 PFC would do with the two legs cut down.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 04/09/2019 10:58:10:

I would have thought the 3mm or so of the scaffold fitting would flex more than the 6mm or so that it looks like Chris has drawn as the thickness of his top clamp.

.

What makes you think that the plate is 3mm, Jason ?

MichaelG.

[ChrisBParticipant @chrisb35596]

Actually it's 16mm thick at the ends (wedges), and narrows down to 10mm at the centre. So in reality I will need a 16mm thick piece – was thinking…I might try getting away with cutting the 120mm piece on the band saw by turning it? I mean cut a piece up to the saw's limit and then turn the piece a bit more and cut again etc.

Is that material PFC linked above plain mild steel Jason?

[JasonBModerator @jasonb]

More or less and not the nicest to machine.

Your 10mm thick should not flex much, you could always have a larger and thicker washer under the nut to help.

[JasonBModerator @jasonb]

Sorry Michael my brain was thinking of the clamp thickness not the plate but now Chris says his will be 10mm thick I'll stand by what I said

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 04/09/2019 11:43:24:

Sorry Michael my brain was thinking of the clamp thickness not the plate but now Chris says his will be 10mm thick I'll stand by what I said

.

That's fine … I only offerered that as an example of the sort of thing that's available.

MichaelG.

[Graham MeekParticipant @grahammeek88282]

Hi Chris,

Not wanting you to go to a lot of work only to find the project might not live up to your expectations.

You might want to give your location stop arrangement some thought. As I see it, the toolholder has to come out either, forwards. Okay if the work is in the chuck, and the carriage can be moved to the left. Not so convenient if the work is between centres.

Or, to the side, by undoing the clamping lever several turns to allow the toolholder to come out that way. Okay getting the toolholder out, but not so easy getting the holder back in as the plate needs to be lifted whilst doing this.

Fitting a spring under the plate might seem at first glance a solution to holding the plate aloft for re-insertion from the side. However if the angled faces are the same length/height then when the plate clears the toolholder angled face it will also clear the tool post face. The plate is then free to follow the lever due to the friction between the lever and the plate. Thereby loosing its alignment with the toolpost.

As a suggestion, a dowel pin in the plate, which fits loosely in a hole in the toolpost will maintain alignment under such circumstances.

Regards

Gray,

Edited By Graham Meek on 04/09/2019 16:19:22

[ChrisBParticipant @chrisb35596]

Thanks Jason and Michael, thinking about it I'll go for mild steel as suggested, I can use 20mm flat bar for the top plate, as that's readily available at the supplier close by.

Gray, the intention is to take the tool off from the side, rather than undoing the clamping lever several times, all I would need to do is a quarter turn to ease off the tension and slide off the C-washer located under the handle (shown in the drawing a couple of posts above) Then enough space will be available to lift the top plate and slide the tool off. It's a bit fiddly I know, might think of something else.

Chris

[Laurent VIDALParticipant @laurentvidal70581]

A bit of outside the box thinking here…. Tell me if I am being stupid here but….

The main reason for using a QCTP is to get the tool at the right height without needing shims.

What about if you had a traditional toolpost (not a QCTP) where the top of the slot for the tool in the tool post was exactly at the center height of your lathe and the grub screws to lock the tool in place coming from the bottom side of the tool post rather than the top ? In this situation, the width of the tool is completely irrelevant… the tip will always be at center height…. Or am I missing something here ?

Laurent

[ChrisBParticipant @chrisb35596]

I'm not sure what will qualify a tool post as a QCTP. For me the ability of changing over from one tool to another in a relatively short time without having to adjust the holder is the goal. Shimming the tool in it's holder happens only once during initial setup (talking about insert tooling here) so there's no requirement for adjustment when swapping tool holders.

As to your suggestion Laurent, in theory it is fine, but in practice you would have to take out the whole tool post each time you need to replace a tool, as the retaining screws are at the bottom. Not so convenient.

Ps. Noticed it's your first post, welcome to the forum Laurent!

Edited By ChrisB on 05/09/2019 07:59:09

[JasonBModerator @jasonb]

Laurent, the other issue with having screws at the bottom is most of the cutting force going into the tool is downwards so you will not get as good support than if the tool were sitting on a solid holder. Also as the screw will need to be inset from the end of the holder you will effectively get more tool overhang so less rigid and more prone to vibration.

As mentioned earlier tip heights can vary with inset tools and if using HSS or brazed carbide the cutting edge will not be at the top of the tool but lower and you would not be able to raise this if the top of the clot was on CTR height.

Finally if it is not a QCTP you would need to take the whole tool post off every time to change a tool if screws were at the bottom.

 

Chris, I would have thought it quicker and less of a fiddle to just unwind the handle a couple of turns rather than faff about with the "C" washer. You could still retract the holder towards you once the plate is high enough to let the holder move sideways enough to let the lip clear the main block.

One other thing have you checked how much support the holder has for the odd occasion when the toolpost needs to be angled as there will be nothing under the holder ends when at 45deg

Edited By JasonB on 05/09/2019 09:00:49

[Nick WheelerParticipant @nickwheeler]

Posted by Laurent VIDAL on 04/09/2019 21:31:21:

A bit of outside the box thinking here…. Tell me if I am being stupid here but….

The main reason for using a QCTP is to get the tool at the right height without needing shims.

The main reason for using a QCTP is to quickly swap lathe tools. Even a simple part could need 3 tool changes(face and turning, chamfer, parting tool). Height adjustment is just a natural part of the drop in design of most of them. The OP's design doesn't have that, so the tools will need shimming the first time they are fitted. This will be much easier to do than trying to machine each holder to suitable dimensions.

The thing that makes them quick change is having enough tool holders handy, so that once a tool is set up, you don't need to take it out of the holder. I have 13 for my Dickson copy so far, and buy a couple more each time I buy anything from the various suppliers.

If the post needs to lift to change each holder, why not replace the mounting post from a nut to a cam operated lever like a bike axle?

[JuddyParticipant @juddy]

I made one of these and 10 tool holders: **LINK**

works very well both on an Altas and latterly a Boxford AUD.

[Laurent VIDALParticipant @laurentvidal70581]

Posted by JasonB on 05/09/2019 08:59:28:

most of the cutting force going into the tool is downwards so you will not get as good support than if the tool were sitting on a solid holder.

the screw will need to be inset from the end of the holder you will effectively get more tool overhang so less rigid and more prone to vibration.

tip heights can vary with inset tools and if using HSS or brazed carbide the cutting edge will not be at the top of the tool but lower and you would not be able to raise this if the top of the clot was on CTR height.

Edited By JasonB on 05/09/2019 09:00:49

Very good points! Did not think of these… Thanks Jason!

Posted by ChrisB on 05/09/2019 07:53:27:

Noticed it's your first post, welcome to the forum Laurent!

Edited By ChrisB on 05/09/2019 07:59:09

Thank you Chris!

[Neil WyattModerator @neilwyatt]

I wonder if you could arrange to have two circular wedges. One would be loose on toolpost and sit on the top slide, the other would be above it and keyed to the body of the toolholder.

This could raise a platform to secure the tools in place as Laurent suggests, without any loss of rigidity. A pair of linear wedges could work even better but be less elegant.

Neil

[ChrisBParticipant @chrisb35596]

Posted by JasonB on 05/09/2019 08:59:28:

Chris, I would have thought it quicker and less of a fiddle to just unwind the handle a couple of turns rather than faff about with the "C" washer. You could still retract the holder towards you once the plate is high enough to let the holder move sideways enough to let the lip clear the main block.

One other thing have you checked how much support the holder has for the odd occasion when the toolpost needs to be angled as there will be nothing under the holder ends when at 45deg

Yes Jason, at 45deg, the tool holder will have less support as you pointed out. I calculated the bottom support surface area will decrease by 28%. But, as the top plate applies force to the tool holder at 45 deg (via the wedged top plate ends) , this should result in the tool holder being pushed both down and towards the tool post body. In other words the tool holder is supported both from the bottom and back faces… right? So I suppose the loss of rigidity will not be so much noticeable – I hope!

Regarding tool post entry and exit routes,I could take the top plate off as suggested, or use cam lever (not sure if clamping force of a cam is comparable to that of a fine thread). But I have (yet!) another design in mind – to the drawing board for design no….4, or was it 5..!

[ChrisBParticipant @chrisb35596]

This the latest amendment to the plans to allow for releasing the tool holder to the side, and without removing the top plate off.

Added three tenons to the tool post block which will engage in slots on the tool holder. This will locate the tool holder for repeatability and prevent the holder moving rearwards.

The top plate wedge and tool holders are slotted with matching grooves. The idea is that to release the tool holder, I release the threaded handle ( half a turn maybe) and slide the top plate rearwards ( the plate centre hole is slotted to accommodate for this). When the top plate slides back the tool holder is disengaged from the "teeth" on the wedge and can slide to the side.

I guess it's not easy to explain but hopefully the drawings can make better sense…or not!

The below drawing shows the tool post in the closed and tool engaged position (left). Unlocked and tool disengaged position (mid) unlocked and tool exit to the side (right)

[Nick WheelerParticipant @nickwheeler]

I think you've gone backwards: that's added a lot of extra machining to each toolholder – you need a lot of them, so that's important – that doesn't justify its existence. That's why I like John Stevenson's suggestion to reverse the dovetails on a more traditional style post, and put the male dovetail on the holders.

[thaiguzziParticipant @thaiguzzi]

Way over complicated.

The whole point of making a QCTP and holders is you make the complicated post once, and the easy (easier) to machine holders multiple times.

A la Dorian/Aloris type clones.

I'm not one to talk because i have (19) and machine Dickson clone holders….

Again, have a look at the American MLA 23 design, so so simple, yet so so effective, and easy to put a location function in if required.

[brickyParticipant @bricky]

This is my toolholder based on the Pratt-Burnerd design

[Graham MeekParticipant @grahammeek88282]

This is a solution I made in the late 1980's before going back to a 4 Tool Turret, based on George Thomas's design.

Regards

Gray,

[Author]

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