Does a threaded mandrel like this exist?

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BHuij

BHuij

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I am working on a slightly oversized chess set. The pieces all have a base diameter between 1" and 1.5", and each one has a hole drilled in the base that I will fill later with weight before putting felt on the bottom.

I'm struggling to figure out the best way to hold these pieces on the lathe. I have a Nova chuck with standard 2" jaws (too large to grip my 1.5" stock). I bought a set of spigot jaws, the smallest ones I could find, and they'll fit inside a mortise that's 1" in diameter. I thought that would be good enough, but the pawns in particular are so thin in the walls around a 1" hole in the base that the expansion pressure necessary to hold them still tends to crack the wood.

I tried using my worm screw that came with the chuck, and drilling a smaller 3/8" hole in the bases instead. It held fine, but was difficult to thread in straight, so it caused a lot of wobble when the tailstock support goes away at the end of the shaping process for each piece. It was also difficult to remove, and because it requires my 2" jaws to hold in the chuck, it posed access problems to the base when I was trying to sand.

So far my best results have come from turning a tenon on the wood down to 3/4" for my largest ER32 collet. Then I can drill a hole (I used a 10mm bit but there's lots of flexibility there) through that tenon and deeper into the workpiece as well. I can then flip it and mount in my collet chuck, turn and sand just fine, it's very concentric and very secure, and after finishing is done, I can just use the bandsaw to chop off the tenon.

That works okay, but it's tedious and wastes wood.

I'm imaging something similar to this screw arbor. A threaded base in the neighborhood of 10-12mm or so would work great for the size of pieces I'm turning. I don't really need it to be permanently attached to its own MT2. It could literally just be a bar that I grab in my collet chuck, has ~10mm length of threading at the end, and ideally some kind of washer or flared bit behind the threads for the base of the workpiece to abut against, so things stay aligned and concentric on the lathe.

Does such a mandrel exist?

If not, would it be realistic to make one out of something like 5/8" brass or aluminum rod? I have dies, though no fancy floating die holder that fits my tailstock or anything like that.
 
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It didn't occur to me that I could properly clamp fully threaded rod into the collet chuck - no issues doing that vs smooth rod?
 
Thanks, I was in bed all comfy and I saw this post and had to respond. Yes a mandrel like this does exist except you'll need a good caliper too. Check out @stainlessbottlestoppers.com (Stainless bottle stoppers) and under the tab "ACCESSORIES" you'll see mandrels and inserts. That's what you'll need to get yourself going. Get the mandrel and brass inserts and a 1/2" Forstner bit and use a good caliper to check for sizing. I use these mandrels for the PSI Jumbo Crochet Hook kits and the mandrels work great. Also they work great for bottle stoppers and bottle openers. Use a good Epoxy like system 3 T88 and you should be good. Good luck on your adventure.
 
BHuij said:
It didn't occur to me that I could properly clamp fully threaded rod into the collet chuck - no issues doing that vs smooth rod?
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Probably not a huge issue. You're turning very small pieces, so you likely won't be putting a whole lot of stress on things. Alternatively, you could buy the mandrel I linked to which lets you choose different size threads and corresponding mandrel shafts that have a smooth section with only the tip threaded like these: https://www.pennstateind.com/store/PKTC06.html
 
Okay cool cool. I think in the interest of being a cheapskate, I'll try some hardware store 3/8 threaded rod with a couple of nuts jammed together and a washer for the "base", stuck in my collet chuck. If that doesn't work as well as I hope, the stainless bottle stoppers products seem like a solid next choice, and they're not expensive.

Since ideally I'm not probably unmounting and remounting these chess pieces much, I think I'll skip the threaded inserts for now and just find the right size of hole to drill for the threads to self tap and hold snugly.
 
Check out the YouTube videos done by Mike Peace. A few years ago, he did a series of videos on making chess pieces, and as I recall, one of the episodes dealt with the problem of holding blanks on the chuck. I believe that he made a screw chuck that he held in a scroll chuck and that use a small diameter screw - smaller than the typical woodworm screw.

Many years ago, PSI offered a special dual-function chuck that could either be configured to use a small screw (1/8" diameter or thereabouts) to grip into a 1 3/8" mortise (it came with a forstner bit to cut that mortise). I don't think they offer that any longer, but it might be possible to find either a used one or something similar from some other vendor.

One of the issues with chess pieces is weight - a naked turning would typically be pretty light and not sufficiently bottom-heavy to prevent pieces from tipping. So its common to add weight in the bottom of chess pieces. A common approach is to drill a recess in the bottom, and then glue in some pennies that are then covered with a wood plug or with felt. The point is that the addition of weight would disguise the hole left by a screw chuck.
 
Why not make a sacrificial piece with a tennon the size of the drilled hole on the bottom of your piece. Mount the sacrificial piece on your Nova chuck and drill a hole for a screw. Remove the sacrificial piece and put a screw from the back into your Chess piece. Re-Mount the two back on to the Nova Chuck. Just check lengths of screw and your Chess piece to confirm you will not be turning into the screw.
 
Lots of good ideas in here. Thanks all for your recommendations. I'll report back on how well the "bolt with head chopped off in a collet chuck" approach works. Thinking of doing a fairly hefty one like a 1/2", just to minimize the chances of it being bent or otherwise non-concentric.
 
First attempt at using the $2.50 screw mandrel yesterday. It's a single partially threaded 3/8" coarse bolt. Chopped the hex head off with a dremel, threw it in my collet chuck, and added a couple of nuts and a washer to give the wood something to butt up against (and to expose only the amount of thread I wanted to go into the workpiece). This is a piece of jatoba. I had to experiment a little bit with finding the right size of hole that let the bolt threads cut in and get a positive grip without being too tight or risking splitting. For this wood, 8mm was about right. Perhaps a hair tight; I might try a tiny step up for the next one - I have an 8.2mm bit. Or maybe I'll try actually tapping the hole with 3/8 coarse threads after drilling before I mount it on the "screw chuck".

But it's turning very concentrically even without the tailstock, it's gripped in tight, and it gives me plenty of room to work with the wood and not worry about running my tools into chuck jaws or anything. I think this will likely work out great as I turn this chess set.

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