Problem turning cellulose acetate

[FGarbrecht]

Got some vintage acetate blanks and boy are those things slippery. I worked on them using a collet chuck but had to crank down the chuck really hard to keep them from slipping during drilling and tapping, and now there are collet marks on the surface. Probably nothing I can't fix (with an hour or two of polishing), but not a welcome sight as I took them out of the lathe.

 

[magpens]

I have never gripped them in a collet chuck, but I have turned them without problem between centers on my metal working lathe.
I found that low speed was the key .... have never tried tapping or threading, but drilling was no problem.

I realize that my response may be no use to you, but just thought I would join the thread to learn whatever is shared by others.

 

[FGarbrecht]

I have never gripped them in a collet chuck, but I have turned them without problem between centers on my metal working lathe.
I found that low speed was the key .... have never tried tapping or threading, but drilling was no problem.

I realize that my response may be no use to you, but just thought I would join the thread to learn whatever is shared by others.

Haven't done any TBC on the metal lathe, guess I should get a dead center for it. How did you grip it for drilling, use a standard 3 or 4 jaw chuck? I wanted to drill using the collet because my acetate stock diameter was pretty small and I was going for maximal accuracy to avoid a blowout (wall thickness after drilling only about 1 mm or so).

 

[duncsuss]

It sounds like you finish the outside before drilling/tapping the barrel, which is the exact opposite of how I do things. (Not that I do it "right", since there is no single right way of doing it - but there are some ways righter than others.)

 

[More4dan]

Get a straight shank dead center, or make one, you do have a metal lathe. It can then be used with a collet or chuck.


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[FGarbrecht]

Get a straight shank dead center, or make one, you do have a metal lathe. It can then be used with a collet or chuck.


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Yeah, it's on my ever-lenghthening list of stuff to do.

It sounds like you finish the outside before drilling/tapping the barrel, which is the exact opposite of how I do things. (Not that I do it "right", since there is no single right way of doing it - but there are some ways righter than others.)

Actually, I do it your way. Drill and tap first, finish last. In this case the starting material was already the size I needed so no initial turning or roughing out was done, and the surface when I started was already pretty good.

 

[TonyL]

Got some vintage acetate blanks and boy are those things slippery. I worked on them using a collet chuck but had to crank down the chuck really hard to keep them from slipping during drilling and tapping, and now there are collet marks on the surface. Probably nothing I can't fix (with an hour or two of polishing), but not a welcome sight as I took them out of the lathe.

Was it a specific sized collet chuck like 5/8, 1/2, 12mm. etc. ? Maybe the blank was slipping because it was "in between" the relatively fixed size of the collet chuck? As others offered, I don't understand the your sequence. I sure you will overcome the issue.

 

[duncsuss]

Out of curiosity, what diameter was your material? And the collet? Can you take a close up photo of the mouth of the collet?

I don't usually have to crank down hard to get a decent grip on material, when I do it is usually because of heat build up - the drill bit needs sharpening, or some lube/coolant, or drilling speed isn't appropriate, or ... (fill in the missing words)

 

[FGarbrecht]

Was it a specific sized collet chuck like 5/8, 1/2, 12mm. etc. ? Maybe the blank was slipping because it was "in between" the relatively fixed size of the collet chuck? As others offered, I don't understand the your sequence. I sure you will overcome the issue.

Out of curiosity, what diameter was your material? And the collet? Can you take a close up photo of the mouth of the collet?

I don't usually have to crank down hard to get a decent grip on material, when I do it is usually because of heat build up - the drill bit needs sharpening, or some lube/coolant, or drilling speed isn't appropriate, or ... (fill in the missing words)

I have a metric collet set and I used the closest sized collet to the material (13 mm blank, 14-13 mm collet). Heat buildup could be at play, but I do drill very slowly, clear thread often, and dunk the bit in water to cool it every 5-10 mm of drilling depth if it is getting warm. I also drill at the slowest speed possible on my lathe, and I lubricate with water (didn't want to lube with drilling / tapping fluid cause not sure if it would have a dissolving or other bad effect on the acetate blank).
Thanks for all the suggestions.

 

[duncsuss]

Good call not using tapping fluid on vintage materials, it's probably not an issue but when dealing with vintage stuff I stick to water (with a tiny drop of dishwashing detergent) or spray-can cooking oil (PAM or suchlike). Note that some vintage material does not like water (such as casein/galalith).

 

[magpens]

Haven't done any TBC on the metal lathe, guess I should get a dead center for it. How did you grip it for drilling, use a standard 3 or 4 jaw chuck? I wanted to drill using the collet because my acetate stock diameter was pretty small and I was going for maximal accuracy to avoid a blowout (wall thickness after drilling only about 1 mm or so).

I use a 4" 4-jaw chuck (scroll type, not the independent jaw type), but a 3" 3-jaw should work just as well for the smaller stock you're drilling.
I guess you are using the collet chuck to try to protect the surface as much as possible. I don't deem that necessary for my workflow order, since I do the surface turning after I do the drilling. . I also keep my drills very sharp to minimize frictional drag ... I think that is important for cellulose acetate which does not like heat.

 

[DrD]

Did you acetate come to you as round stock? Have you tried wrapping it in Tygon tubing and clamping in collet? Tygon is my go to surface protector.

 

[FGarbrecht]

I use a 4" 4-jaw chuck (scroll type, not the independent jaw type), but a 3" 3-jaw should work just as well for the smaller stock you're drilling.
I guess you are using the collet chuck to try to protect the surface as much as possible. I don't deem that necessary for my workflow order, since I do the surface turning after I do the drilling. . I also keep my drills very sharp to minimize frictional drag ... I think that is important for cellulose acetate which does not like heat.

I've noticed some of my drills cut very quick and clean, some seem to drag. I need to learn how to sharpen them. Add to the list. I do the surface after the drilling, but any marring during drilling just adds to the work so I'd like to avoid it if possible.

 

[FGarbrecht]

Did you acetate come to you as round stock? Have you tried wrapping it in Tygon tubing and clamping in collet? Tygon is my go to surface protector.

Yes, round stock. I thought of using some of that grippy cabinet liner to wrap in the collet but worry that it'll get things out of concentric. Is tygon wall thickness uniform enough to avoid that issue?

 

[FGarbrecht]

One other issue I've discovered is that carbide wears out lots faster than I had anticipated, and if it isn't new can leave surface imperfections that are really hard to get out. I was surfacing some ebonite on the metal lathe and was getting a ribbing pattern and assumed it was because my lathe carriage or lead screw were misadjusted. I took the whole lathe apart and adjusted everything, but the thing that really helped was just rotating the carbide insert in my cutter. Live and learn.

 

[More4dan]

One other issue I've discovered is that carbide wears out lots faster than I had anticipated, and if it isn't new can leave surface imperfections that are really hard to get out. I was surfacing some ebonite on the metal lathe and was getting a ribbing pattern and assumed it was because my lathe carriage or lead screw were misadjusted. I took the whole lathe apart and adjusted everything, but the thing that really helped was just rotating the carbide insert in my cutter. Live and learn.

Are you using metal cutting carbide or carbide made for wood turning? The metal cutting carbides are very blunt and don't do well for wood nor acrylic. You need a sharp edge and at least 20-30 degree edge. Most inserts made for metal have a 7 degree edge. Inserts made for Aluminum will be better but still don't have a truly sharp cutting edge. HSS ground with 20-30 degree relief and clearance angle has worked better for me.

Danny


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[FGarbrecht]

Are you using metal cutting carbide or carbide made for wood turning? The metal cutting carbides are very blunt and don't do well for wood nor acrylic. You need a sharp edge and at least 20-30 degree edge. Most inserts made for metal have a 7 degree edge. Inserts made for Aluminum will be better but still don't have a truly sharp cutting edge. HSS ground with 20-30 degree relief and clearance angle has worked better for me.

Danny


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Didn't know all that. I've been using the carbide insert tools from littlemachineshop for metal cutting, and the main issues have been surfacing non-metal surfaces, like ebonite and alumilite! My experience cutting brass and aluminum has been quite good on the contrary. Now that you mention it, the carbide inserts on my wood lathe tools DO look much sharper than the ones on my metal lathe toolbits.

I ordered some HSS tool blanks from littlemachineshop last week, so perhaps I can improve things once I get some new tools sharpened.

Thanks Danny

 

[bmachin]

I think that your problem may have been that you were at the max diameter of your collet. I may be mistaken but I seem to remember reading somewhere that ER collets hold best when they are compressed, but not to their extreme limits. Thus a 13mm collet holding a 13mm diameter part isn't doing the greatest job in the world and likewise if you squeeze it all the way down to 12mm.

I started with a Beall set for my wood lathe and then built a complete inch set by 32nd's. You need a few more collets this way, but you have the advantage of always having an overlap from one size to the next since each collet grips a range of 1mm.

Bill

 

[DrD]

Yes, round stock. I thought of using some of that grippy cabinet liner to wrap in the collet but worry that it'll get things out of concentric. Is tygon wall thickness uniform enough to avoid that issue?

Yup, I believe it is made to ANSI Standards re wall thickness, OD, ID, Out of Roundness, etc. I just buy 1/2" tubing, cut it to desired length, slit it lengthwise & place it around whatever it is that I need to grip. Has worked well for me over the years - but it is pricey.