Lathe chuck spindle attachment

plate, on a 9" lathe]
Geometrically, a lot of other shapes would work, such as some triangle and wedge cross sections. Of course, the fixed-radius curved-cross-section trepanning tool that you mention probably would be strongest and best for thin cuts. However, at radius 3.25" cutting .25" deep with a .5"-high cutoff blade, it would work to grind a 5-degree [*] side relief (and 1 degree of back relief, per toward the end). Also, you might want to trepan to a slightly smaller radius than the finish ID and then finish by boring, depending on what gives a better or quicker result.
[*] For a trepanning blade of height h at radius r, the interference at the outer bottom edge is about (h^2)/(2*r). With a .5"-high blade, this comes to 0.038" at 3.25" radius and to 0.042" at 3".
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I've snipped DoN's other comments; take them as predecessors to following suggestion: If the ring is for a sun-dial, holes on the back won't show, so you could drill holes .15" deep to seat upon pins in a mandrel plate attached to the faceplate. The pins would withstand shear forces, allowing much heavier cuts than you could take when depending on glue or tape to withstand those forces. One could tap the holes, use loctite and studs, etc, but presumably not worthwhile to do so.

Yes -- you could make one by grinding a HSS tool bit to the proper radii -- including clearance.
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Yes. Keep the lathe speed slow, and the cut depth small to keep the forces down.
Hmm ... for the drilling, you could make a special holder which held a thrust bearing assembly with a bore larger than the drill which you would use to start the hole. You could crank the carriage into position (with the bearing well centered) to maintain extra pressure while drilling, since you don't need the carriage for the actual drilling.
Hmm ... another way to hold it fairly concentric (assuming that your stock is truly round and near the desired size) would be a ring which slips over the OD of the workpiece and (with less than 1/2" radial size around the workpiece) and drill and tap four holes at 12:00 o'clock, 3:00 o'clock, 6:00 o'clock, and 9:00 o'clock and clamp it to the faceplate with two steel bars going from 12:00 o'clock to 3:00 o'clock and from 6:00 o'clock to 9:00 o'clock so they don't interfere with the spindle -- and the ends have to be cut to clear the bed. This, perhaps augmented by the double-sided tape, would hold things firmly in place.
Hmm ... two rings -- one which is a fit on the faceplate, and the other on the (larger) workpiece, held together with bolts might make getting things centered a bit easier.
Anyway -- with these approaches, you could use higher spindle speeds than you would find safe with just the tape.
In any case -- use alcohol or acetone to scrub down the surface of both the workpiece and the faceplate to make sure that they are both free of oil and grease for maximum adhesion of the tape.
One of many ways. I've suggested some others above which take more time making fixtures, but which make sense if you are making multiples of these (e.g. the scales for your sundials).
It depends. super glue forms a rather brittle joint, so if you have an interrupted cut or otherwise bump things you could break the bond. The double-sided tape -- especially sufficient area of double-sided foam tape -- will give a very good grip, and be more immune to shocks.
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Yes -- the torque needed goes up fast with increasing diameter.
The rotary table and a "slot drill" (two flute endmill) of perhaps 1/4" diameter will probably work fairly well.
Yes.
Actually -- you *could* -- barely -- with modified jaws. It is just more difficult to make jaws for a 4-jaw than soft jaws for a 3-jaw which is already fitted with two-piece jaws.
Think of the special soft jaws available for the Taig/Peatol lathe. Those will handle a workpiece significantly larger than the chuck body. For a 5" chuck -- just make large pie jaws to replace the hardened top jaws -- *if* the machine comes with a chuck with two-part jaws.
Hmm ... also, this sounds like an argument for a gap-bed lathe. The first few inches of the bed can be unbolted and lifted out to allow working with a larger diameter workpiece. There is some debate whether the removed section can ever be put back as precisely as it was positioned when the bed was first ground, but there are things where the gap bed is a winner.
Lots of ways to do it -- depending on the lathe, and how many of the same size workpiece you are making.
What you are making is relatively thin so you don't have to worry about it clearing the carriage.
The larger the diameter, the more grip surface you have between the double-sided tape and the workpiece and faceplate.
But in any case, I would not consider 550 RPM to be a good idea.
First -- if the tape does let go, it could throw things rather hard.
Second, 6.5" diameter means 935 SFM, which strikes me as a bit fast unless you are using something like carbide tooling and a free cutting mild steel like 12L14.
Based on the cutting speeds chart for HSS tooling in the Jorgensen steel book:
Steel SFM --------------- 1018 125 12L14 300 4140 120 (annealed)
Stainless steels below Steel SFM --------------- 304 75 416 160
Enjoy, DoN.

. That is getting tricky...
I like that.
Acetone for the faceplate. Alcohol for me...
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I have not considered that aspect... I do. All the time :-)
Those will handle a workpiece significantly larger than the The problem arises with the Taig also. None of the chucks will hold a 4" piece. I do the insides with a boring head on the mill and finish on the Taig. [ ... ]
No, no! I did say I shall try with *4"*. Yes, 550 rpm (the lowest the Taig will go) is way too fast for that too, but I have managed so far. The only way it works for facing is a sharp HSS tool with a small point radius. And a very slow and steady hand as one gets to the outside. To do the inside I need to bore only about 2" diameter. OTOH there is probably no point doing that as the mill method works just fine and it will provide me with only limited information about how the big piece would behave. Granted. But if I followed that I would be cutting nothing bigger than 1" diameters. The frightening thing about it is that to face the piece (1018) in question (8" diameter) one should have a lathe with low speed of 60. Back to cranking the handle...

I will save this for future reference, thanks. Right now my plates are pre-fabricated but who knows, in future this may be the way to go. ' I routinely attach the armature to the back of the face just that way. It took me a few attempts to reliably drill a 0.15" hole without going right through (the current faces are 0.189" thick) and to drill deep enough to get at least two threads of 10-32. In fact this was another way I contemplated but I did not think of the shear pins which would certainly simplify matters.
Much obliged, this is helpful.

I am rapidly going off the idea of purchasing a lathe with a flange, or indeed anything "Craftex". Ask me why. Hint: I just bought a Craftex band saw.
I should have kept the old RedNeck lathe...:-)

I've been reluctant to suggest the way I machine large arcs, but you seem to have some experience now.
I attach a pivot post to the table of the mill, drill the blank to fit on it, attach a long handle and manually rotate the blank into the end mill. Yes, the end mill is likely to grab and try to spin the work, more so if there is any play at the pivot. That isn't too serious while the blank is still a polygon because the end mill quickly reaches a gap. Once the arc is nearly continuous the depth of cut has to be very small. I use a small endmill at low speed, extend the quill all the way down and don't lock it so I can knock the handle upward, and set the drive belts quite loose, but it's still as dangerous as working freehand on a drill press. The worst one I've done this way was a circular tee slot, after the milling force damaged my undersized rotary table.
I mostly do this to round the ends of linkage bars and stop before the arc is tangent to the straight edge. wider hinge part was first clamped upright in the milling vise, with a shaft through the hole to position it atop the jaws, and milled almost to size across the top. A larger diameter piece could be clamped to an angle plate. The disk will vibrate if not well supported close to the cut.
If the disk can be clamped firmly to the mill table, raised on spacers, it can be cut nearly to size much more safely by rotating it slightly between cuts. The frequent reclamping is incredibly tedious but it would get your 8" disk close enough to finish with a light cut on the 9" lathe.
For even larger circles I set them up on a shaft and round them with an angle grinder, held so it crosses at an angle and spins the disk as it cuts. That's how I shaped the front tire for the sawmill. I haven't tried yet, but I think a disk could be turned fairly accurately on a wooden frame with a lathe bit on an X-Y table which moves crosswise, parallel to the axle. Think of an old foot-pedal grindstone frame. You could spin the disk with a sanding drum in a drill.
The right way is probably to buy the largest rotary table that fits on your mill. The disadvantage compared to a gap-bed lathe is that you can't detail the edges as much, you'll be limited to end mill profiles like vee grooves and corner rounders.
jsw

Those would be the GT18 steering sectors?
I have to digest this...
I think you mentioned this to me before. In fact I believe it was the inspiration for this marvel of technology:
I did not have as much luck facing with the grinder. I made some plastic jaws for a chuck on my woodlathe and used an angle grinder with a sanding attachment but for some reason it did not work too well either. I have a feeling that the thing has to spin at a lower rate than 300 rpm to give the grinder chance to work (I am talking face work here).
Still, the on-going problem is the *inside* of the doughnut.
I am certainly considering it as a viable option. Realistically I cannot get anything bigger than 6" rotary table on my mill and even that is probably pushing it. OTOH if one could do things that way it is a $1000 difference in capital expenditure :-)
BTW can you put a motor drive on a rotary table so it turns at a constant rate?

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O.K. But the latter *after* you are done with the machining for the day. :-)
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Hmm ... I would have to go down and set up the chuck with the extruded jaws to be sure -- but remember that you can bore a recess in the jaws up to within perhaps 1/4" from the ends of the fingers.
But you could *make* pie jaws from solid aluminum plate at need to have the extra reach needed.
And if the swing of the lathe is the problem, add one or two riser blocks between the headstock and the bed. Those riser blocks will stack if you have (or make) two of them.
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Hmm ... replace the motor with a DC motor and a proper speed controller, or a small three-phase motor and a VFD to run the motor at perhaps 1/4 speed. (about 140 RPM).
O.K.
Or -- you would swap in motors which could be run slow enough to get proper speeds.
Hmm .... the current motor has what RPM? 1800 RPM, 3600 RPM? There are 900 RPM (four pole) motors which will get your first reduction in speed.
Or -- to a proper variable speed motor -- either three phase, or DC.
Or -- use uncoated carbide inserts to survive the higher speeds.
Enjoy, DoN.

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There is a stepper motor drive for the little Sherline rotary table, which can be used with a controller/keypad:


With a CNC milling machine, you could even use it for engraving the time markings on your dials.
Enjoy, DoN.

The Taig swing is 4-1/8" ...
I considered that. Those who know better than I told me that the rigidity declines quite significantly. Machining 4" with the existing setup is a constant struggle with rigidity as it is. Or for the same money just get a bigger lathe. I went through this some time ago. The torque at the low speed is a big problem with the Taig. Even as it is I have to lean on the motor some times to stop it stalling. It is what it is: A little lathe for little things.
I tried those. I thought they were horrible. Got much better results with properly ground HSS.
This is all done on the un-modified Taig:
(well, just the step - much milling there also) There has been a learning curve :-)
In any case, I really have no idea what is a reasonable expectation of a good finish achievable by a lathe of whatever size. This 1' beast was turned by a professional. The concentric ridges are apparent. Can one ever get rid of them? Can one make them look uniform without a power-feed? Should one go back to facing with sandpaper and just do the edges on a lathe/mill? What is the meaning of life...

Some rotary tables can be motorized to run continuously while milling, but I expect that some of the light duty RTs should probably just be used for positioning.
I was using a motorized RT for a while, and it seemed to work very well (hobby, not production speeds & feeds). I used a small Oriental Motor gearmotor, chain and sprockets and a Phase II 6" horizontal RT. The RT was turning very slowly, less than 2 RPM, maybe considerably slower. It's a method I wanted to try, for cutting disks from sheet/plate stock without center holes.

That piece fit on the lathe after sawing it roughly to size. I clamped the square blank flat on the bandsaw table with tee bolts to cut off the corners. Then I set the saw upright and followed a scribed circle as far as the wide blade allows, then opened up the kerf with a chisel to make clearance the next cut.
The upright pivot post is held in the vise, the disk rests on 1-2-3 blocks which raise it above the jaw tops. Tee slot clamp bolts clamp the disk onto the 1-2-3 blocks, leaving a small space in between to mill tangents to the OD. It's slower than sawing because of all the reclamping but doesn't risk cutting in too far by accident, and leaves only a little metal for the lathe to remove.
The ladder-shaped frame of my sawmill is the model. Both wheels needed truing and the front one considerable flattening. I used the crosspieces at the inner ends of the wheels for tool rests, ie to hold the grinder steady.
You could make a similar frame out of wood by laminating 2x4's with the ends alternating to form glued finger joints. I'd make two side-by- side rectangular bays, the second providing a tool rest for faceplate turning.
The faceplate could be a large pulley faced with plywood. The bearings on the motorcycle wheels were tight enough to use one as a lathe faceplate, though the protruding axle interferes. If you did that you could drive the tire by friction or remove it and run a vee belt on the rim. I used the sprocket only because I needed to transmit several horsepower, it required a separate countershaft.
I think an X-Y table would be stiff enough for a tool rest. I acquired one plus the headstock from a scrapped SB lathe and a brake lathe tailstock to build a large wheel lathe, but haven't needed to set it up yet.
jsw

So, it bears further consideration. I guess the next question is "How fast can you rotate a rotary table?" :-)

I should be able to the very same tomorrow (once I found where the knocking noise is coming out of the Craftex). BTW, when you got your band saw, did you change the oil in the gearbox right away or did you trust the Chinese and left it for a year or so?
Got it.
Another one to digest :-)
I was thinking that if I return to red neck technology I would probably make the ring spin horizontally this time. But anything will be considered. The important thing is to spin the work piece quite slowly otherwise the grinder works quite inefficiently, at least on the face. The RedNeck lathe v5.01 went at less than 100 rpm and could have gone slower. I found that an X-Y *vise* was capable of holding lathe tools quite firmly and take large cuts. Here it is with a boring bar holder I made:
I have to add that the wobble was all in the chuck: The spindle had a runout of only about a 0.001" :-)

That 4-jaw setup was actually quite impressive. Extra points for feeding the boring bar and cutting metal while holding the video camera to make the video.
That 4-jaw chuck looks like the one that's supplied with the 9x20 lathes. The wobble doesn't exist on the lathe spindle because the spindle includes a raised shoulder feature to register the chuck at a nearly perfectly square position.
I read quite a few remarks from disappointed new 9x20 lathe owners, wrt the 4-jaw chuck. I found the chuck to be suitable for a lathe of that size and power. It's not like a 9x20 is intended to turn a 50 pound workpiece at 1000 RPM.

There aren't any multi-part bearing assemblies (roller, ball) in the 6" Phase II RT that I used, just plain polished (finely ground) steel sufaces against machined cast iron, with the parts well-oiled with 80 or 90W gear lube. Since old lathes could spin hundreds of RPM (with lighter oil), I suppose a RT could be run fairly fast if it's designed and built well enough. The table's support surfaces are significantly different than a lathe spindle as the two machines are designed for different purposes/applications.
Some RTs are 40:1, others are higher turns per rotation. Worm reductions typically have slow output speeds although heavy duty models can handle some serious loads. If one were inclined, the worm of a RT can be disengaged in many models (or removed), so the table stem could be driven from the back side or bottom, depending upon the orienation (of the RT, not the operator).
As long as the RT isn't routinely subjected to the side loads of turning down diameters, push knurling and other typical lathe operations, a RT may be suitable (just speculation) for occasional cutting operations similar to facing cuts on lathes.
If the table's stem support/bearing surfaces wear, the accuracy of the RT is diminished, so an overhaul may be necessary, possibly requiring boring and a bushing or sleeve installation.

Very nice!
I traded away my X-Y vise and couldn't remember how far the ways protruded beyond the jaws, so I didn't mention it. The one you have looks to be of better quality, I bought mine around 1980 and it may have been cast from leftover Great Leap Forward backyard iron.
jsw

I bought a second-hand Delta 4x6, so I'm not sure what the gearbox had in it originally. It was full though black when I changed it, after reading warnings here. The new oil has stayed fairly clean.
It has adjustable blade guides and the Delta logo on some small parts so they did add some value over the generic saws. I strengthened the base and put on larger wheels but otherwise it was reasonably well made and cuts straight as long as it's on the flat basement floor. When I use it outdoors on the uneven driveway I have to move it around until both sides of the handle end of the base touch down at the same time, and then check that the blade rises perpendicular to the table with a square. That's OK since the outdoor cuts are structural steel for welding and don't need to be as accurate. Indoors it cuts square vertically to within ~0.005" per 1".
jsw.

I did not complain while I was using it. I got it on sale - cannot remember where.