3DP chuck spider backstop

[petertha]

Not sure if I labelled the fixture gadget properly. Hopefully the pictures convey the intended application. Gripping relatively thin parts in the nose of the chuck jaws so they are self aligned to the chuck face turning plane. Good for facing repetitive parts because of the datum much like parallels in a mill vise. I have a cheesy set of offshore aluminum ones which are A) not accurate B) never quite the right stack width for the job C) use magnets to attach to chuck which I'm not fond of because they attract swarf. These allow you to make your own parallels & just insert them into the slots. The 3DP shape holds them captive so the cant fly out. Of course you could make them bog or small, 3-jaw, 4-jaw, whatever. Of course, be careful about clamping delicate parts & use light machining passes. Its not as good as machineable collets or pot chucks, but useful as intended.

[mcostello]

Excellent idea.

[crueby]

I printed some spiders a while back, in several thicknesses.  Only problem was they softened if the part got hot during turning.  Wound up having sets laser cut from different  thicknesses  of aluminum, works great.

[petertha]

They got hot, interesting. Didnt even consider that. I forgot to mention my 3DP spider itself does not contact the part or the chuck. I made my own parallels from 0.125" thick aluminum. I know, not the best parallel material. Anyway the parallels obviously make flush contact with the chuck face & part face, but there is air gap between the spider faces. I did that to avoid any swarf getting embedded in the PLA & mucking up alugnment. Its basically a glorified carrier to orientate the parallels which do the back-stopping. Now I can envision some heavier cutting could transmit heat from parallel to spider & thus soften the PLA. So a good prcautionary note. Thus far I have just been skimming relatively light duty parts. I don't trust a limited grip length of chuck jaw nose at the best of times.

[petertha]

Wound up having sets laser cut from different  thicknesses  of aluminum, works great.

Can you show me a picture? I'm interested.

[crueby]

Wound up having sets laser cut from different  thicknesses  of aluminum, works great.

Can you show me a picture? I'm interested.

Here's what I had laser cut. Each set has three thicknesses, so I can stack them to get different offsets. Got a couple of each type for the 3 jaw and the 4 jaw. The ones with the holes in the middle are handy when through drilling thin parts, at least up to that size hole. The holes/surrounds limit how small a part can be gripped. The other type has a narrow junction in the middle, good for holding smaller diameters not being throguh drilled. I also got a larger set for the big chuck, same styles just larger diameter and thicker since the jaws on that chuck are deeper. Its handy to have thicknesses that are not even multiples of each other, gives more combinations when stacking. All depends what your total jaw hieght is and whether you are using inch or metric stock. I looked around online to find a cheap place to get them cut, prices vary a lot. The slots for the jaws are a little wider than the jaws so they don't bind. Oh, and I got extra sets after playing around with cart quantities when ordering - sometimes there is a minimum amount for setup, so getting three sets might cost about the same as two, etc.

[steam guy willy]

Hi These are some the plastic spiders I got printed up by the Local Hackspace group that I am a member of ...quick and easy to file to shape and fit with arkwaed mountings .....some of them are also fixed with Cs screws to keep them in position ?!
Willy

[cwelkie]

I like your idea of using a printed holder for metal parallels.  This avoids the pitfalls of "plastic variability" due to heat, wear and compression when used for the actual spacer.  I may have to print a couple holders for a set of 3" ground parallels I've got.  They usually get used for this purpose with magnets but a 3DP holder would be less fussy.

[maury]

THis is a great idea, but it's not limited to lathe chucks

Sometimes when working with a casting it's hard to hold it for that first cut on the mill. Here is an example of a printed helper for vicing up a bearing cap.

[petertha]

I like your idea of using a printed holder for metal parallels.  This avoids the pitfalls of "plastic variability" due to heat, wear and compression when used for the actual spacer.  I may have to print a couple holders for a set of 3" ground parallels I've got.  They usually get used for this purpose with magnets but a 3DP holder would be less fussy.

I sent my friend the print files just to save him the modelling effort. Not that they are difficult but after we chatted just so happened to match what he was going to do. Buy a cheapo set of 6" Chinese parallels & cut them in half yielding 4 sticks of matched width. Apparently his are ~0.126" so pretty close. I thought that sounded a bit wasteful but he pointed out a set for ~50 CAD on Amazon, including a plastic case LOL. I could buy plain steel cheaper but certainly not tool steel, nevermind the hardening. I guess as long as the cut was kept cool it should be OK. Food for thought.

[Minh Thanh]

Not sure if I labelled the fixture gadget properly. Hopefully the pictures convey the intended application. Gripping relatively thin parts in the nose of the chuck jaws so they are self aligned to the chuck face turning plane. Good for facing repetitive parts because of the datum much like parallels in a mill vise. I have a cheesy set of offshore aluminum ones which are A) not accurate B) never quite the right stack width for the job C) use magnets to attach to chuck which I'm not fond of because they attract swarf. These allow you to make your own parallels & just insert them into the slots. The 3DP shape holds them captive so the cant fly out. Of course you could make them bog or small, 3-jaw, 4-jaw, whatever. Of course, be careful about clamping delicate parts & use light machining passes. Its not as good as machineable collets or pot chucks, but useful as intended.

That’s a great idea !
I had previously tried to come up with a tool that could do something similar, but I hadn't found a practical design ,  for even smaller diameters (3, 4, 5, 6, 8 mm, etc.).
Based on your idea, I might be able to make some improvements... hopefully, it works out.
Thanks for sharing ! 

[Charles Lamont]

An alternative backstop for smaller diameters is, in its simplest form, a sleeve fitted in the spindle taper that carries a flat-faced plunger.

I have recently made the more complicated Radford/GHT version. The sleeve is fitted with long tube and a nut so that it can be fixed in the hollow spindle. The nut is long enough to stick out of the changewheel cover. Inside the tube, a long rod has an adjustable plunger screwed onto the business end, and a long thread at the back for a second nut that adjusts the amount of projection. The plunger is fitted with a disc of a diameter to suit the work (not shown, as not yet made). For smaller work a different plunger is used with flat-faced rods to fit within the chuck jaws. At the back end, the threaded rod has a keyway to allow for a clamping screw.

 

[Minh Thanh]

An alternative backstop for smaller diameters is, in its simplest form, a sleeve fitted in the spindle taper that carries a flat-faced plunger.

I have recently made the more complicated Radford/GHT version. The sleeve is fitted with long tube and a nut so that it can be fixed in the hollow spindle. The nut is long enough to stick out of the changewheel cover. Inside the tube, a long rod has an adjustable plunger screwed onto the business end, and a long thread at the back for a second nut that adjusts the amount of projection. The plunger is fitted with a disc of a diameter to suit the work (not shown, as not yet made). For smaller work a different plunger is used with flat-faced rods to fit within the chuck jaws. At the back end, the threaded rod has a keyway to allow for a clamping screw.

 

The issue is that the homemade lathe and the small lathe I bought don't have a taper in the spindle.
I find Petertha's method to be the most suitable for any lathe—it's probably the simplest solution  ... the only thing left is to figure out how to adapt it for even smaller diameters., A diameter of about 4 or 5 mm is fine; anything smaller would require a custom-made tool.

[petertha]

An alternative backstop for smaller diameters is, in its simplest form, a sleeve fitted in the spindle taper that carries a flat-faced plunger.

That looks like a nice tool. I should make something similar. I have a stop accessory for my 5C collet chuck, which if I recall, need to be careful if  repetitive parts are not the exact same diameter because that changes the collet closing on the taper & thus distance relative to bed, resulting in non-equal thicknesses if you were going off the same target dimension. Luckily I discovered that after only a dozen or so parts  Your tool solves that I think.

Anyway yes I thik the key word is smaller diameters. If you are chucking a large diameter + thin profile, then it has some chance of getting cocked up on a small diamter stop, whereas the spider parallels provide 3 edges of contact so I think is going to sit on that in a more planar manner.