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Off center turning

John Torchick

John Torchick

Joined
Jan 24, 2010
Messages
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Location
Cleveland, Tennessee
Yesterday I was turning cork for the foregrip on a spinning rod that I am building for a door prize. Everything was going OK until I took the grip off the mandrel. It was off center! Had sand it down but I'm not happy with the results. I'm going to glue up another set of cork rings and start over.
The cork rings are glued up with Titebond III and set for 12 hours. I use a mandrel from Mudhole, a rodbuilding supplier. It is a 14" long steel mandrel, 1/4" diameter, both ends are inletted 60 degrees. One end of the mandrel goes into a chuck and the other end is placed over the live center. I try not to put a lot of pressure on the cork to keep from flexing the mandrel. Maybe I need a shorter mandrel? I'll hold off turning until I hear from you folks. Any and all help is appreciated.
 
Hard for me to imagine a cork turning mounted on a 14" long, 1/4" mandrel NOT flexing if you just push on the center with a finger. Your mandrel should be only as long as necessary to hold the piece, and no longer. Can you grip it further up in the chuck, with the cork held close to the tail end?

I have no experience turning cork but I know you would need either razor sharp tools or a tool you can use with minimum pressure on the piece such as a sanding disk in an angle grinder.
 
I do a lot of off center turning

some deliberate, some not. A few thoughts:
- Might be nice to have a queen anne leg type end which would be a deliberate off center turning. Go with the flow!
- Mount the drive center end of the mandrel in a long nose chuck if you can add some extra length. This will noticeably stiffen things up.
- Use a chuck or maybe a fixture with a set screw on the tailstock end and use tension not compression to bind the two ends
- If you use compression, use as little as possible
- Use the highest speed possible
- Use a very sharp, honed spindle gouge and take delicate ice cream scoop peeling cuts ALONG the axis with no pressure to the center
- Don't change or adjust your mounting until you are done. Any relaxing of the mounting will change the axis
- The 80 grit gouge is your friend. Maybe seal the cork for turning and prior to sanding.
- Grind up some cork to fill in the bad spots. No one will notice (maybe.)

When I tried to make rod ends I ended up with THESE so I gave up and sold them as magic wands.

All this may help, or not...

Good luck, Jerry
 
I don't use any turning tools but use drywall screen for the initial shaping and then use fine sandpaper for smoothing the finish. I have been considering using a piece of threaded rod that is just a bit linger than the grip. Thanks for the replies.
 
backing for the media

John,
I understand the use of drywall mesh, what type of backing are you using? I would think a straight backing on the mesh and a light touch should work. Like a 2x4 the same length as the handle that has been through the planer. Also some washers or something at each end that will help keep the size constant the length of the handle by not allowing the straight edge to go deeper. If you are trying to do it with your hand, I don't think most of us can apply pressure that steady.
Bill
 
Been there, myself, John.
From my encyclopedia of rod building mistakes I have made 😉--
1) headstock and tailstock are not lined up quite right. This is something we're supposed to check regularly, but I usually forget.
2) mandrel is not square in the chuck. We've all had a small diameter drill bit get in between the prongs on a drill chuck and I think it's possible for the same thing to happen with a mandrel.
3) Morse taper or the spindle hole it fits into may have some gunk on it.
4) You may have a bent mandrel. The steel rods from hardware stores are often not straight and although rod building ones start out that way, they can be bent. The Mudhole ones may not be as resistant to bending as the Backlash mandrels.
5) Since you know how to make grips and don't use gouges, I doubt you're putting enough pressure on to flex the mandrel.
 
Turnning

Hi, Dean! Have all points covered except for the Backlash mandrels. Might spend a few $$$$ and get a Backlash mandrel. What size do you use? Most of my grips are on the smaller size so 1/4 inch works for me.
I use the drywall screen without any backing since some of the work has contours rather than straight lines. I'll try to get some pix of a grip to show you folks. I cut a strip and hold it over the cork while turning. When it gets a lot of dust on it, I hold it over the DC hose and clean it. I try to put the minimum pressure on it. A couple of days ago, I experimented and cut a piece of threaded rod just long enough to hold the cork with about an inch held in the chuck (wrapped with a couple of turns of tape to protect the chuck jaws). Seemed to work OK as the cork grip came out with the same amount of cork all around the hole. Hopefully, I can do this same thing with longer grips. Got a couple of ideas I might try. Will report on them is successful or not.
Thanks for the replies!
 
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Roll the mandrel on something truly flat, like table saw or pool table. If it's bent, it'll show. Backlash mandrels aren't expensive and if you really want a different than standard length, they'll make one for you.
Plumber's mesh abrasive on a roll (180 grit) is another option for speed sanding.
 
John Torchick said:
Yesterday I was turning cork for the foregrip on a spinning rod that I am building for a door prize. Everything was going OK until I took the grip off the mandrel. It was off center! Had sand it down but I'm not happy with the results. I'm going to glue up another set of cork rings and start over.
The cork rings are glued up with Titebond III and set for 12 hours. I use a mandrel from Mudhole, a rodbuilding supplier. It is a 14" long steel mandrel, 1/4" diameter, both ends are inletted 60 degrees. One end of the mandrel goes into a chuck and the other end is placed over the live center. I try not to put a lot of pressure on the cork to keep from flexing the mandrel. Maybe I need a shorter mandrel? I'll hold off turning until I hear from you folks. Any and all help is appreciated.
Click to expand...
John, I suggest that you get an adjustable Pen Mandrel, that way your mandrel will be only as long as your cork. Then get a Mandrel-Saver, a live center with a hole that just fits the mandrel, and that way when you bring up the tailstock, you don't put pressure on the mandrel, the pressure is on the cork.
Just a suggestion.
 
Turning cork

I don't use backing. I just place the mesh over the cork and turn. For places that are "formed," I use a thin piece of mesh and use my fingertip as a backing to place a bit of pressure for abrasion.
Al, I'm familiar with the Mandrel Saver at Penn State. I saw it used at a turning demo last month. I'll look at the pen mandrel but it might be too short as most of my cork grips are 6-1/2 to 7 inches long. Right now I cut a piece of 1/4 inch round stock, like drill rod, and it's working OK. Cut it to fit and the steel doesn't flex. The old mandrel was aluminum.
 
John:

I've read through the entire thread and MY gut says it's flexing a bit (1/4" x 14"!)... I'd recommend you try a 3/8 mandrel on your next go-around.

TL
 
collet chuck

Al's right about holding with a pen mandrel chuck, but I would recomment using a collet chuck like the Beall chuck or on the cheaper side get a 1/4" morse taper collet and make yourself a drawbar. The morse taper collets can be had from "Best Tool" or the "Little Machine Shop". These can be had in all different sizes like 3/8 for bottle stoppers etc. I have had pen mandrels that flexed in the adjustable pen collets but were a solid as a rock in the larger collet chuck.

Vernon
 
Mandrel

In most cases a 3/8 mandrel would be too big. The cork rings I use for fishing rod grips have a 1/4 hole in them. Right now I am building an ultralight spinning rod whose butt section is just a bit over 1/4 inch. The 3/8 mandrel would require gluing the rings, reaming the grip, turning and then shimming the rod blank to fit the grip. Let me mention that reaming is a tapered fit to fit the rod blank. Drilling the hole bigger is really not a good option. So far, the steel rod is working OK. I goofed though; the original mandrel was steel, not aluminum, according to a magnet. Many thanks for your replies and suggestions!
I'll try to get some pictures of the process of making and forming/turning a cork grip.
 
You can make a 1/4" mandrel. I would use 1/4" 1080 steel rod, a little softer than drill rod so it will be easier to cut the threads. Cut it to whatever length you want, then stick in a collet chuck so you only have about 2" sticking out. Use a file to "face"/square up the end, then use a 60 degree center drill to get your center. Next is the hard part, use a block of wood with sandpaper with coarse grit, 60 or 80 is what I use. With the lathe turning slow, sand the end down about .02 with a slightly rounded end. This will take a while, do not apply excessive pressure, or you will bend the rod. Next is using the die, I would use 1/4-20 threads, the coarser threads seem to cut easier, and a few less turns. I just thread one end, the same as the 60 degree center end.

I cheat and do it on a metal lathe, a little faster, because I do not have to sand the rod down to size. But have done it the way I described, basically making a super long pen mandrel.

Marvin
 
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