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Holding Knurled Stock In A Lathe

Ripthorn

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#1
I knurled some stock last night with my new Shars scissor knurling tool, and the tool has some side to side play in it, so it actually pulled the piece out of concentricity while doing so. The knurl turned out well, but it spun wobbly after that. I would like to flip it around, hold on to the knurled part, and turn the remainder of the stock concentric with the knurled section. However, in my tests, the chuck marred the knurling, as I am using 6061. I tried some .003 brass shim stock, but it still crushed the knurling. Any ideas how to hold it? I don't have a collet chuck, and the piece is too big for a standard 5C or R8 collet anyway.

On a related note, I think I will always knurl with a live center in the tailstock to avoid this issue from now on...
 

brino

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#3
Hi Ripthorn,

Do you mean the knurling wheels had side-to-side play?
I would first check that the knurling tool is actually on centre. If it was not, it might try to force the work up or down and actually bend it.

Although the clamp type knurling tools are much more forgiving than the type you just press into the work. The live centre is a good idea for knurling anything sticking out of the chuck more than one diameter. A fixed steady or follower rest could also be used.

The only suggestion I have for holding onto a knurled part is with a collet chuck. Depending on the lathe spindle and the size of the work piece you could get an ER-32 or ER-50 collet system like these:
http://www.bealltool.com/products/turning/colletchuck.php
http://www.bealltool.com/products/turning/bigchuck.php
For only a few parts it may not make sense, but I find I use my ER-32 collets very often.

I was going to suggest a heavy paper wrap over the knurls, but it might not be better than the brass you already tried.

-brino
 
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joshua43214

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#4
Might want to step back and review your original set up.
A scissor style tool should not push the work off center. I also use the Shars knurling tool and have not had this issue with it.
If this turns out to be a bell mouthed chuck, keep that in mind when running at higher RPM. You don't want to lose any teeth when something comes out of the chuck.

I use 0.010" brass shims for protecting work. Never had any luck with the thinner stuff. Never tried to protect a knurl in 6061 though. 0.010" does work fine on steel knurls
 

Ripthorn

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#7
Thanks for all the info guys. I had a realization that a bump center might be able to help some as well, in terms of regaining my concentricity of the knurled side. Have any of you fine people used one before? I was able to just fiddle around and get it concentric enough for what I am doing. I'm just making some knobs for my guitar that I'm building, so tolerances are pretty loose by the standards of those here.

A split sleeve is a good idea. I would probably also do well with a collet chuck, as I turn lots of smaller diameter stuff. I will look into these on future projects.
 

mksj

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#8
A couple of things you may consider.
1. I did not have much success in holding smaller knurled knobs/round stock in a 3J, both from a being able to hold it and keeping it parallel when the piece was short (like 1/2" or shorter). A 4J usually has coarser jaws that mar up the knurl, 6J would be better in distributing the load if you have the $$$. I had problems with the pieces shifting when turning and not being able to hold the piece parallel to the chuck face in my 3J. I do not have this problem with a collet system, and I do a lot of small items where less than 1/4" is being held in the collet.

2. I use brown paper bag cut in strips to wrap around delicate pieces, usually one layer in a collet type holder, 2 or 3 layers at each jaw on a 3J or 4J. Do not use masking tape, the piece is guaranteed to twist and move with tape. Brown paper shopping bag material lightly compresses and has a high frictional capacity. I have no damage of knurls in different materials using the paper bag and a collet system, especially in softer materials, but it has also worked well with my 3J and 4J. I tried brass stock at one point, it did not work as well for me. Brown paper bag shim also works well in a collet system where you trying to hold a piece (like your knob) which is between collet sizes, I use the larger with a single layer of brown paper bag, works like a charm.

On the collet system, if I need two layers, I cut 2 strips, just slightly shorter than the diameter of the piece, wrap them around the part like an onion peel, then insert into the collet. If wrapped as one piece in a spiral, it may not clamp symmetrically.

3. Of note if you decide to do more turning of small short stock. Use a collet style chuck to hold the piece, only applies to stock 1" and smaller. This is what I routinely use, it works well with one caveat. When you knurl, you displace the material and the diameter gets larger. If using a 5C collet system, if you started out with something like 3/4" stock, it will now be about 0.02" larger in diameter after knurling, and will no longer fit the 3/4" 5C collet. You need a full set of 1/64 increment 5C $$, I found this out the hard way, as I accumulate more over time.

4. If you only do this occasionally, and on short stock, consider an ER-40 system, you can buy or make a Hex (for 3J) or Square (for 4J) ER-40 block holder for about $30. Chuck it in in your 3J or 4J and use an ER-40 collet which has a much wider clamping range.

5. Last but not least, if you want to end up with a knurled rod that is 3/4", you need to under size the rod slightly before knurling. Also, sometimes the knurling can be a bit rough on the hands or too pointed, I either take a light cutting pass to take off tops of the points, and or lightly sand the tips, and put a small bevel one either edge of the knob.
 
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chips&more

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Active Member
#9
Knurled 6061 is not going to like being held no matter what you do. It is too soft and any attempt to chuck/hold it will probably show some kind of attempt at it in the knurl. Maybe make a plastic split bushing to hold it? Best thing is to machine your steps so the last step is the knurl…Good Luck, Dave.
 

Billh50

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#11
I have used a piece of cereal box wrapped around a knurled rod with good success. the cardboard will pack itself into the knurl and is thick enough to help protect it. The pvc pipe would also work as the points of the knurl will dig into the inside of the pipe.
 

Wally

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#12
That scrap of PVC pipe saved the day. I just got a set of ER32 collets and naturally, the first thing I wanted to use one for is just under an inch in diameter and knurled. (replacement knob for my drill vise). Cut a piece about 2" long, cut a 1/4" slit in the side and it worked perfectly. Also worked to protect the knurling when I screwed it onto the handle shaft - tight fit and took a pair of channel locks. Many thanks. I was so disgusted and the solution was so easy.
 

Cadillac STS

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#13
Another vote for PVC pipe with a slit in it to hold the knurls if it is close to size. If a different size is needed bore out a piece of nylon or similar to fit.
 

4gsr

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#14
Another tip to try. Knurl from left to right if holding stock between the chuck and tailstock center. This way your live center will keep the stock from moving in the chuck while knurling. And I mentioned live center, too!
 

RJSakowski

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#15
The PVC is a good idea. To avoid marring any material, the wrap has to be softer than the work. Brass is harder than 6061; lead would be a better choice. You may be able to get away with softening some aluminum sheet by heating. Plastic cut from a milk jug could also work as a wrap. I have used multiple wraps of masking tape in the past. The wrap has to be thicker than the features you're trying to protect. Otherwise clamping will just punch through and contact the hard jaws.
 

savarin

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#16
I use masking tape, about 3 turns and clamp in the three jaw, it packs into the voids in the knurl and holds fine.
I like the idea of pvc pipe and will do that next time.
 

Cadillac STS

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#20
Don't, why would one place a knurled surface in a part holding device afterwards, please explain.
Depends on the project but sometimes it is not possible to do knurling last. For example there is something I make that has a knurled body right up to a tapered end. So with the taper there is nothing to chuck up to be able to knurl.
 

benmychree

John York
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#22
Brass makes a poor wrapping for chucking, it is too hard; soft copper is best, such as that used for flashings on roofing. As far as plastics are concerned, if I was going to make a split sleeve for holding the knurled part, I'd use Delrin, as it is a good deal harder than PVC, etc.
 

Cadillac STS

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#23
Another reason very often to chuck the knurled part is the clean up the lead in and out of the knurling, the start and finish that is not sharp and crisp as a half roll to the side of the start/finish when only partial knurl is made.
 

Wreck™Wreck

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#24
because I'm a hobbiest not a pro and didnt think the job all the way through or I made a cockup and had to repair it
Not criticism merely a question, often such operations are required when the person that designed the part failed to take into consideration if it may be produced by conventional means as drawn.
You have to do what you gotta do in that case.
 

savarin

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#25
Not criticism merely a question, often such operations are required when the person that designed the part failed to take into consideration if it may be produced by conventional means as drawn.
You have to do what you gotta do in that case.
Yep, that sounds like me except for the drawing part, a few sketches on a bit of scrap paper is my usual modus opperandi. :laughing: