Turning disc of phenolic

OK, so here's the situation: We make this weird instrument (see
formatting link
. It has a rosined wheel, turned by hand
by the player. For about a year we've been making the wheel from a linen-filled
phenolic, which is wonderful - no moisture
sensitivity, much less machining time. The only downside is how long it takes
to scrape the wheel so it has no runout.
So at breakfast my wife asks me why the wheel always needs to be scraped, i.e.
why doesn't it come from the lathe with no
runout - and I have to say I don't really know. I then postulate that it's
because the wheel and shaft inevitably exhibit
some chatter when turned on the lathe. and I wonder what I can do about it.
The shaft is about 7" long, and the wheel is 7" diameter x 3/4" thick phenolic.
The shaft diameter is 5/16", O-1 drill rod,
held between a 5/16" A3 collet and a live center. The wheel is about 5" from
the wide end (in the collet) mounted on a
threaded region, supported by a collar. I'm using a South Bend 9".
Any suggestions for how I might turn this material with less chatter? For
example, what side rake and back rake angles are
best for phenolic resin? A slow speed seems to help, but doesn't eliminate the
problem. The shaft would still be relatively
"floppy". I could turn the wheel on a thicker, heavier shaft, but then it
wouldn't be being turned on the actual shaft that
will be used.

Your help appreciated, as always,
Alden
Reply to
Alden Hackmann
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If the standard sized bore is 5/16" why not make a mandral from a heavier piece of round stock, say 3/4". Make a section that is turned to just under 5/16" Make two larger flanges to support the wheel your turning that will it on this section in addition to the thickness of the disk itself, and then thread the remaining portion so a nut or threaded flange or collar can be snugged up to the disk. Pl;ace the reduced sectin of the round stock in a collet, and use a live center to support the opposite end. Aftere completion of machining the disk round, use a ream to enlarge the hole to 5/16". I would imagine you could make the intitial hole 5/16" to start with as well.
Becarefull of that phenolic your using as its known to be a carcinogenic material the dust / smell is highly irritable to nasal cavities and lungs. It was so much of a hassle to just even drill the stuff where I used to work with having to have special ventilaors etc that we soon just stopped doing anything with it in house. I like working with it myself.
formatting link
. It has a rosined wheel, turned by hand
linen-filled phenolic, which is wonderful - no moisture
takes to scrape the wheel so it has no runout.
i.e. why doesn't it come from the lathe with no
because the wheel and shaft inevitably exhibit
phenolic. The shaft diameter is 5/16", O-1 drill rod,
from the wide end (in the collet) mounted on a
example, what side rake and back rake angles are
the problem. The shaft would still be relatively
wouldn't be being turned on the actual shaft that
-- Visit my website:
formatting link
foundry and general metal working and lots of related projects. Regards Roy aka Chipmaker // Foxeye Opinions are strictly those of my wife....I have had no input whatsoever. Remove capital A from chipmAkr for correct email address
Reply to
Roy Hauer
First off, what surface(s) are you hand-scraping, and to what are they fitted?
I would suggest that you consider simply mounting the phenolic blanks in OD jaws and and profile both sides, then mount on your shaft or mandrel and take a skim cut across the OD to clean it up.
The shaft you are using is pretty thin and flexible, that may be where some of your chatter is coming from.
LE phenolic can be somewhat abrasive so if you are using HSS tooling it will get beaten up pretty fast. Carbide if used instead should be *un*coated as the coatings require a honed edge and the phenolic really wants a sharp tool and fairly large postive rake. My personal favorite for this is polycrystaline diamond inserts from Valenite. I run the tpg221 sized ones for composites and they last forever and give real sharp edge.
You will also find that much of the aroma from turning phenolic goes away when cutting with a very very sharp tool. I think most of it has to do with burning at the cutting edge.
A beefier mandrel as suggested would be a good way to go. This is how we used to make sheaves, three operations - profile first side, profile second side, and mount on mandrel and turn OD.
Jim
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Reply to
jim rozen
That would be the OD. I know this instrument. For my sins, I was talked into producing a wheel for it from materials found by the builder. The rim of the wheel is coated with rosin, and bows the strings as the crank is turned by hand.
The wood he selected was not seasoned at all, and expanded and contracted significantly with humidity changes -- along the grain length. This resulted in the volume produced raising and falling with the rotation of the wheel.
Another problem was the variation of the finish possible on the end grain vs the side grain, resulting in an unpleasant rasping sound beyond that introduced by the "trumpet" -- a vibrating bridge designed to sound raspy. :-)
I suggested that he get some wood which was a slice out of the center of the tree (starting with a naturally rather round piece, so the expansion would be equal. He never did find something which was reasonable, so I turned him one out of Plexiglas. That was perfect from my point of view (and that of all others who knew him), as the polished edge of the Plexiglas would not hold the rosin, and thus produced a very quiet instrument. (He was never able to play it well, you see. :-) I'm sure that you are making them for people who *can* play them, and I have since heard some, and been amazed. My friend was not a good poster-boy for the instrument.
Unfortunately, he fixed that by gluing some wood veneer around the rim, with a diagonal joint where it closed, which worked surprisingly well.
I would consider a custom point for the live center with a socket to hold the shaft and let the center get close to the wheel to give it better support. (Or set up a steady rest close to the wheel to control the vibration.)
I gather that the shaft can't be swallowed deeper into the collet.
That sounds like an excellent suggestion. And I'll bet that it gets rid of some of the end-grain fuzz which you can get from turning phenolic.
Or support closer to the wheel.
I think that the sides are not really critical, assuming that the hole is square to the surface. (Though it would probably look nicer if they were faced, too.
Enjoy, DoN.
Reply to
DoN. Nichols
Alden Hackmann wrote (clip) Any suggestions for how I might turn this material with less chatter.(clip) ^^^^^^^^^^^ I suggest you support the wheel on a round steel jig, with three pins on it, say 3/4" diameter, at 120 degrees around the center. Three holes in your phenolic blank will hold it with no chatter and very little runout. If you think the holes look bad, decorate them so they fit with the ornamentation on the hurdy-gurdy (viol?)
BTW, I love that kind of music.
Reply to
Leo Lichtman
I really don't know. It sort of resembles it in smell though. The linen or canvas lamiunated stuff is supposedly made with formaldehyde. Thats whats supposed to be so bad for you. I have some nice piece of this stuff, from 1/16" thick to 3" thick, and everything in between, some in 36 x 36 inch sheets, and some sheets a lot larger. It used to be a mainstay in aircraft, but its nbot quite a popular as it used to be. No matter what, I still like working and using this stuff.
-- Visit my website:
formatting link
foundry and general metal working and lots of related projects. Regards Roy aka Chipmaker // Foxeye Opinions are strictly those of my wife....I have had no input whatsoever. Remove capital A from chipmAkr for correct email address
Reply to
Roy Hauer
The outer rim is what gets scraped, not in the usual machine-tool scraping manner (I think, not ever having done that) but with a heavy wood plane blade or a cabinet scraper. The reason it gets scraped is to smooth it for the contact with the strings. The strings rest on the wheel, which is rosined and acts like a bow. To keep the tone even, the wheel must have very little runout: if there's variation in the diameter, the string pressure on the wheel varies, and the sound changes. Instead of getting a nice smooth "ummmmmmmmmmmmmmmmmmmmmmmmmmmmm", it sounds like "MMMMMM-mmmmmm-MMMMMMM-mmmmmm".
Initially when making the wheel I put the sawn blank on a faceplate to turn it down to the basic diameter, and to drill and tap it (5/16"-18). There is less chatter in this situation, but of course the shafts have a little runout, and the tapped hole is never exactly perfectly square to the blank - so between these two, there's always some runout in the wheel when it's on the shaft. Consequently I make up matched sets of wheels and shafts: once a set has been assigned to an instrument, it's not interchangeable with another set.
My past experience with carbide, at least with metal, is that the poor old 9" SB lathe wasn't rigid enough for it. Suggestions (besides a bigger lathe)? I'm using an Aloris QC toolpost.
That would be nice. ;-)
The sides are less important - just the OD (which is not square, but is cut at several degrees angle.)
Thank you,
Alden
Reply to
Alden Hackmann
Hmmm. I would stay away from a tapped hole to mount it to the shaft, for the reason you say, this does not provide good locational accuracy for the finished assembly. A better design would be a straight bore in the phenolic, and a round section on the shaft. The shaft could have a shoulder at one side and threads on the other, a nut could compress the phenolic up against the shoulder.
Tapped holes do *not* work well if you are trying to minimize radial runout. Just taking the part off the shaft, and putting it back on, will give you a few thousanths of error right there.
Jim
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Reply to
jim rozen
This doesn't work with the system we're using, for esthetic reasons. ;-( However...
How about a wheel that is tapped (half) and reamed (half)? Would the phenolic threads hold up? I would think so. Would the half that's bored straight be enough to stabilize it? That's the way we used to do it, with a nylon insert in a wood wheel, until we had several incidents of the nylon threads being stripped.
Alden
Reply to
Alden Hackmann
I would say that if the phenolic is about an inch thick now, one half inch of threads would probably do fine. A half inch of straight shaft would certainly center it up properly.
I would suggest putting the blank in a chuck, and profiling one face, and then drilling and tapping the entire thickness. Then go in with a boring bar and bore out to the shaft diameter.
The final step would be holding in a mandrel, *centered* on the finished bore, with a center hub as I previously described, and turn the OD. Then the OD will be exactly concentric with the bore.
Jim
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Reply to
jim rozen
The drive rod is winding up.
Bore a 5/16 hole in a faceplate, and GLUE the disk to some blocks to make it parallel to the faceplate. Put the blocks out near the edge to be machined. It won't chatter that way because it's coupled to the large mass of the faceplate.
Yours,
Doug Goncz, Replikon Research, Seven Corners, VA Unequal distribution of apoptotic factors regulates embryonic neuronal stem cell proliferation
Reply to
Doug Goncz
manner (I think, not ever having done that) but
is to smooth it for the contact with the
To keep the tone even, the wheel must have
on the wheel varies, and the sound changes.
like "MMMMMM-mmmmmm-MMMMMMM-mmmmmm".
I've heard that -- with a buzz added from wood end-grain extending with humidity. :-)
[ ... ]
*Tapped* hole? You mean that the wheel threads onto the shaft? How do you tap it? In the lathe, just after drilling, while still on the faceplate? If you go to a drill press, you're introducing an additional place where error can come in.
I would instead of tapping it, drill it slightly undersized, and ream to size in the lathe (or bore before reaming, to make sure that things are on-center), and make that size a light press fit on the shaft. Then I would use a tiny end mill, or a reciprocating saw, to make a short radial slot from the center hole, and drill the shaft for a pin which would be pressed in and prevent the wheel from ever rotating on the shaft. I would have a thread on the shaft just *after* the wheel, and a screw-on nut (perhaps with pin spanner holes) to secure the wheel to the shaft. The shaft *should* have a shoulder to assure that the wheel is square to the shaft, and to resist the thrust of the nut.
Is the wheel permanently mounted to the shaft from the time it is machined to final installation? If it comes off for intermediate operations, and there is no pin or other feature to assure alignment between the shaft and the wheel, each removal and replacement can introduce more error producing runout.
1) Tighten the gibs on the compound and the cross-slide to minimize the give there.
2) Use the largest tool shank you can for the size of toolpost and holders. With a 9" SB, you must be using an AXA Aloris, so the maximum shank is probably 1/2". (BXA lets you use 5/8", buying more rigidity, but I think that is too big for a 9" SB.
3) Minimize the extension of the tool from the holder. (There is a fancy Aloris tool holder which offers support to allow you to clear a live center while turning. The top view is somewhat like this:
+------+ | \ | O \ | \ | O | | | | O |\| | | | O ( 0 ) | | | O |/| | | | | +----------+
This gives you a bit more rigidity if you can't crank the toolpost any closer to the workpiece. I use one of these when threading using carbide insert tools, and may get another someday.
There is also a tool holder which has clamps for insert tooling directly on the holder -- no extra shanks to deal with. More rigid, but it limits your choice of inserts to whatever is supported by that holder. There are two variants, one with positive rake, and one with negative. I have the negative rake one since it works with the inserts which I use elsewhere. (With chipbreaker grooves which turn it into an actual positive rake, but you get thick tool inserts with no undercut for relief, as that is provided by the negative rake.) Unfortunately, these are the triangular inserts, and I don't know whether the suggested PCD (PolyCrystaline Diamond) inserts are available in that format. They would be a good choice, in any case. These holders are double-ended, offering one insert for turning, and one for facing in the same tool, only requiring transferring to the other dovetail on the toolpost.
4) Minimize overhang in the compound. Ideally, the toolpost should be centered over the pivot/mount of the compound to the cross-slide.
5) Don't use the inexpensive sets of five insert holders (parallel left, angled left, neutral, angled right and parallel right), as they tend to be rather wimpy, and to use thinner inserts, without a proper Carbide anvil supporting them, so they break much more easily, and otherwise lead to chatter.
Isn't it crowned? That was how the ones which I made were produced. (Back before I had such nice tooling and machines to work with. :-)
Best of luck, DoN.
Reply to
DoN. Nichols
The nut doesn't have to *look* like a nut. It can be a cone, with pin holes or grooves (which could be disguised as decoration) allowing a special wrench to tighten it firmly.
Add that to an anti-rotation pin (as I just suggested in another branch of this thread), and you assure that it goes back in the same position.
How thick is the wheel at the hub? What pitch are the threads? I think that you are using a wheel of about 1/2" thickness, which is not really enough if half of its length is taken up by threads. And the rather coarse threads which would seem to make sense in phenolic would result in not enough of them to really trust.
Otherwise, this is similar to how a lathe's spindle centers its chuck, with a register shoulder and threads for the force.
Do you ever encounter a player who likes to turn the wheel backwards most of the time? Do you have problems with it coming off under those circumstances?
I think that this answers your question. :-) It just isn't long enough to devote half of the thickness to threads and half to a reamed hole for centering.
Does the shaft stick out much beyond the hole? If not, a cone-shaped nut could look rather nice, and be a lot stronger than the phenolic, let alone than the nylon.
BTW Have you looked into using Delrin (acetal) for your wheel? It is available in both Balck and natural (a sort of light cream colored white. and is a lot more durable than nylon.
Good luck, DoN.
P.S. Can you trim your line length a bit? Standard length should be no longer than 72 characters, to allow some levels of quoting before they start to get folded. I've been having to re-format your lines so the whole of the text is visible in my editor, instead of part of it hiding beyond the right margin. Since some are worse than others, I suspect that you are using a proportional pitch font for posting (which means that ASCII graphics will appear distorted -- including my earlier attempt to show the shape of the special Aloris tool holder which would be more rigid than what you are using. If it was unintelligible, go back to look at it with a fixed pitch font selected, such as Courier (always a safe choice. :-)
Reply to
DoN. Nichols
I would think that from an engineering perspective, even a half inch thick wheel could be mounted on a small shaft this way, with a threaded shaft with a 'register diameter' on it, the same way that a lathe chuck fits on a threaded spindle.
I would propose a design with 0.200 of very snug register diameter, and 0.3 inch of threads, proabably about 20 threads per inch or so, maybe 24. LE phenolic is actually really really strong and threads up nicely. Key to this design is cutting the threads in the blank fairly loose, so that the register diameter does the work of centering the shaft.
Another approach would be to eliminate the threads altogether. I would suggest performing linear knurling (not cross hatched) on the shaft in the central region where the wheel fits, and then boring the hub to be a very tight press-up on the knurled section. It sounds to me like the driving torque is pretty modest and I could imagine that a properly done press-up onto knurling like that could have the .313 shaft twist up before the joint slips.
Oh. Great minds think alike! :^)
The knurled, pressed-up joint would solve that issue nicely....
Jim
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Reply to
jim rozen
The wheel is drilled and tapped on the lathe.
There is a shoulder, 1/2" diameter.
The press fit/pin/nut are a cool idea, but the wheel needs to fit through a hole that has minimal clearance (1/32" - 1/16") around the wheel. I don't think the body would stand up well to the shaft being pressed in.
The shoulder does this, I assume. The wheel is removed from the shaft after machining.
[much useful advice deleted]
Ah, there's the rub - as it is, I've had to slide the toolpost back so ~1/2" is hanging out. I probably need to make the cool flat cross-slide from Metal Lathe Accessories.
Um - a little lost here. Could you point me to some MSC Big Book pages showing the wimpy stuff and some showing the good stuff? I'm afraid that I wouldn't know a good insert holder if it fell on me... but in any case, I guess I know which inserts I'm looking for, so I can let that choice help me to find good holders.
The surface is flat, with a small radius at the edge to keep the string from being cut by a sharp edge. I've tried instruments with crowned wheels - not a good sound. The surface is much better flat, like the hairs of a bow.
Thank you for your comments,
Alden
Reply to
Alden Hackmann
Hmm - I'd need to think about that.
3/4" thick wheel, 5/16-18 threads
Then 3/4" should be fine.
Cool - got it.
It's quite an unnatural motion. A very few players use a quick back-and-forth motion sometimes for a special effect. We have occasionally had difficulties with the wheel coming undone when the crank is removed, as players often do when storing the instrument. To this end, we have been milling a small pair of flats on the exposed end of the shaft for a 1/4" box wrench. (The old method was a pair of Vise-Grips(TM) - yuck!)
The shaft extends about 1.4", into the head bearing.
We need the rosin to stick, and for the material to be completely stable regardless of the humidity.
Sorry - I'm using ASCII, but the screen was really big. Hopefully my resizing to 80 columns has solved this.
Alden
Reply to
Alden Hackmann
Sorry - I should have specified the body of the instrument, not the wheel. I'm sure the wheel and shaft would do fine with this. The situation is that we need to be able to install the shaft and wheel in the instrument and remove it again fairly easily.
To give you a better idea of the instrument, here's one of our progress pages:
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A few photos down, VG37 is being drilled and tapped for the bearings and shaft, and in the next photo, VG37 is sitting with the wheel installed. Once the soundboard is positioned, we'll take it out again, and glue on the soundboard. We'll put it in again to position the bridge and the keybox, and we'll take it out for finishing, and put it in again to string it up.
Thanks for your ideas,
Alden
Reply to
Alden Hackmann
Greetings Alden, I don't know about the rosin sticking, but acetal resin absorbs almost no water. It is vey stable with changing humidity. In fact, I make scuba parts out of it and the lack of water absorption was one of the main reasons for choosing this material. It is a good engineering plastic and can be used for bearings, knobs, etc.. Soon, I will be sending out to several people small pieces of this plastic that are just scrap to me. If you want some let me know. All you pay is the postage marked on the box. About 4 dollars. Cheers, Eric
Reply to
Eric R Snow
I can think of several ways to disguies it as decoration.
Better than I thought. With half of that as register cylinder, that leaves 3/8" length, which is over six threads.
I think so.
[ ... ]
Isn't the action of the "trumpet" (vibrating bridge) sensitive to the direction of the wheel? Could a player opt to silence it by turning backwards for a while? (Yes -- there are other ways to silence it, but they require taking a hand from the crank, or the keys for a little while.)
You could also use a hole through the diameter and a pin-wrench to hold it from turning.
I could also see a bayonet style connection between the crank and the shaft, so you have to press the crank towards the body to disengage the fittings.
[ ... ]
O.K. So you've got bearings on either side of the wheel, instead of two bearings mounted to a cylinder between the wheel and the crank.
You've just gotten an excellent offer on some samples in a second followup to this. Get some, and try the rosin to see whether it sticks. Your stability with humidity question has already been answered.
Perhaps you have been thinking of Teflon, which is a sure guarantee that the rosin won't stick.
But it might help to sandblast the rim after turning it with Delrin (acetal). I've never actually tried to get it to hold onto rosin.
[ ... ]
That has made things a *lot* nicer. I'm using an editor which is trained to cut the lines at 72 no matter how wide the screen is, so I don't have to worry about that (except to turn that option *off* if I need really wide lines. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
O.K. So it should be on-axis, then.
[ ... ]
O.K. I can see that. But a gentle press fit, not a firm one might be do-able, with the pin dropped into a hole through about 2/3 of the shaft's diameter at the last moment before entering the wheel. (I presume that it would otherwise have problems feeding through the bearing at the crank end.
Thus a need to be able to assure the orientation of the wheel relative to the shaft on re-assembly in the instrument.
That would probably make it a lot better for your purposes.
O.K. Let's see what I can find (but the first clue is that the wimpy ones come in sets of five, sometimes boxed, sometimes in a wooden stand with holes for the five cutters, two spare screws for attaching the inserts, and one or two hex keys (Allen wrenches) for the screws.
Names like Valenite and Carbaloy are found on the good ones, plus some from Israel (Iscar). Let's start on page 617, upper left-hand corner, for the PCD tipped inserts. (These would last a lot longer and do a cleaner cut on your composite wheels. (From those, you can select holders to fit the inserts available. (*Don't* use these on iron or steel, however, it will convert the diamond to extra carbon in the steel alloy, which doesn't help you at all.
If you use carbide, don't use the TiN coated ones (or the other coatings), as it results in a slight rounding (dulling) of the edge. Good in working steel, but bad for composites.
You'll have to stick to 1/2" square shanks, thanks to your toolholder. Look for ones with carbide anvils as separate replaceable items. it gives better support to the inserts. Valenite holders start on page 622. Some styles are not available in the 1/2" size, which is another thing to control your choices. (Find a combination of inserts and holders which will work with your lathe and your materials.
Valenite is only one good brand, and happens to be first in the catalog. (Reverse alphabetical order by any chance?)
Page 633 includes a diagram of how at least one style of good holder goes together.
The cheap sets are shown on page 553, and I've found them to be inadequate even for a 5" Emco-Maier Compact-5/CNC. Once I found a good supply of the diamond inserts which fit the tools which came with it, I was quite happy, and have totally retired the cheap sets.
I hope this helps. I'm putting the catalog back on the shelf while I've still got some circulation to my legs. :-)
O.K. But angled to match the angle of the strings?
You're welcome. I hope that they help.
Good Luck, DoN.
P.S. My wife recognizes your name from some of her newsgroups (and/or mailing lists).
Reply to
DoN. Nichols

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