Turning Archive 2005
Darrell in Oakville
>The Pole-lathe Pen: A Tale of High Adventure and Crazy Ideas.
Executive Summary: I made a pen on a pole lathe.
For those of you with loads of time on yer hands, and an interest in funky turning practices, read on...
It all started one day whilst I was perusing the APT website at www.bodgers.org.uk and saw how many varied and interesting items were being turned on pole lathes. Chair legs, cups, bowls, plates, spoons, and so forth. This inspired me to try turning a pen on my pole lathe.
First off, I needed a way to mount the pen mandrel between the dead centres on my lathe. The mandrel has a #2 Morse taper on the drive end (for headstock spindle) and a small dimple on the tailstock end. The pole lathe uses a pair of dead centres. The tailstock end will fit fine, but the head- stock end of the mandrel needs to be mounted in something to allow it to be held on a dead centre. I think I need a drive block, which will hold the pen mandrel and provide something to take the pole lathe's drive rope. How about a MT2 socket drilled into a block of hardwood? I googled and searched EBay, and found a MT2 reamer cheap.
The wooden drive block was made on my General lathe at home and, whilst I'm certain I *could* have made it on my pole lathe, I am also certain it would have been much more difficult and not nearly as accurate a job. I turned some scrap beech into a spool shape to hold the drive rope from the pole lathe. Then I bored a hole using a 5/8 brad point bit in a drill chuck mounted in the lathe tailstock. This will accept the pen mandrel's MT2 shank. I chucked the MT2 reamer in a bit brace and reamed the hole.
I mounted the new wooden drive block with the pen mandrel in it on the lathe and checked for concentricity. Not good. Wobbles like crazy. Shakin' like a dog tryin' to pass a peach pit sideways. Not to worry, I have some experience with reaming holes for windsor chair legs, so I know how to adjust a tapered hole. I carefully noted which was the "high" side and reamed a bit more, while pressing the reamer away from the "high" spot. After a couple of adjustments, the drive block assembly turns smooth and concentric.
I made up a set of curly maple blanks for a pen, plus a set of "dummy" blanks from beech, for testing. I have a Mark I Bodger's Muddle mounted on my lathe. It's a transverse mounted twin-bow recoil mechanism rather than a traditional long pole. See the Plans section on the APT website for details. The only serious concern I had was the potential for bending or pulling off the mandrel rig. The drive rope is pulling "mostly" down, but a bit away from the lathe, so it could possibly pull the "tailstock" end of the pen mandrel out of the lathe. In the past I have had problems with the ropes on the bows breaking, which would be a disaster with the pen mandrel, because there is no recoil, just the drive rope pulling the work off the lathe!. So I decided to cut a sapling and use the lathe as a true pole lathe. Fewer moving parts = fewer potential problems.
Another concern is how tightly the work is held. Too much pressure from the centres will cause the pen mandrel to bow, as it's only a skinny 7mm steel rod.
And if all that were not enough to worry about, then how about pulling the pen mandrel out of the block when I'm done turning? A MT2 will hold plenty tight on hard steel where there is no compression of the parts, but if one piece is wood, then the taper may get so tightly locked I cannot seperate the assembly. The only thing I could think of is to bore a hole through the headstock end of the wooden block so I can insert a punch to drive out the pen mandrel. This hole must not interfere with dead centres holding the assembly in the lathe. I drilled a 1/4 inch hole from the socket side of the blank, out through the other end, at an angle so as not to hit the centre point. A 6 inch piece of 3/16 stainless steel rod will serve as a knockout bar. This drive block may end up as a single-use item, s I may have to destroy it to get the pen mandrel out...
Rather than try to take the blank from square to round on the lathe, I will first make it sort-of-round with a chisel and block plane. The rounder it is when I start, the better it will 'turn' out (pun intented).
The Bodger's Muddle was set aside, and an ironwood (hop hornbeam) pole was substituted as a recoil. This worked fine, as one would expect because after all, it IS a pole lathe.
I mounted the beech test parts on the mandrel and chucked the assembly in the lathe. It spun quite nicely. I tried turning down to a smooth cylinder, and encountered my first problem. Too much flex in the mandrel shaft. That, combined with the tool rest being FAR too far away from the work, resulted in some very nasty behaviour. I was afraid I was going to bend the pen mandrel shaft.
I tried loading the curly maple pen blanks on the mandrel, thinking that I would reduce the risk of damage to the shaft by using it less. This was even worse, because the figured maple is prone to catches where the grain is diving. Egads, this is so bad I might have to give up on the whole idea. It's time to go to the beach anyways, so I left the problem till later. Hopefully I will have an inspiration or something...
Here's what I did after some serious thinkin'... I dismounted the drive block assembly and shortened the mandrel so that it would hold only one half of the pen. This means that I'll have to turn the two pieces separately but the shorter mandrel will reduce deflection a lot. I also built a closer tool rest, just for turning half a pen. This rest was screwed solidly to the lathe bed.
Now the turning went MUCH better. I was able to turn down the first half of the maple blank with only a wee bit of tearout left. I didn't want to chase the tearout any farther for fear it would make the turning too small to use. My tools are 'reasonably' sharp, but far from prefect, as I'm working with some pretty basic equipment. I have a 1 1/2 inch roughing gouge, a 1 1/4 inch skew, and a parting tool. For sharpening I have a 1000 grit slipstone.
The second maple blank was going well, until a grain reversal at a weak point tore a huge hunk of wood out, right down to the brass. Perhaps I can find the lost piece and glue it back on? I got down on my hands and knees and fought with the ants under the lathe, but alas! I could not find that bit of wood. Good thing SWMBO wsn't still hanging around with the camera. Lacking a piece to glue back in as a repair, I had to abandon the experiment.
Tenacity (or as *some* would say "stubborness") being one of my virtues, I refused to give in to total defeat, and went back to the beech test blanks. I finish turned them sanded and burnished with a hand ful of shavings. Wow! The beech takes on a beautiful polished sheen simply with burnishing! I applied some friction polish to the pieces and ended up with a very acceptable looking "pen". There were no tubes mounted in these blanks, so the turning is a bit off centre, and the hardware won't stay in place, but this is for the "You Get The Idea" (tm Roy Underhill) effect.
I will try and rescue the maple pen and finish it on the pole lathe next weekend. Wish me luck, eh!
Meanwhile, back at the ranch, er home...
So I have a set of mangled curly maple pen blanks. One has a big hunk torn out of it, right down to the brass. The other was turned too skinny in a vain attenpt to chase down some tearout. Now what do I do?
My wife Kathy has more experience turning pens than I, so I begged for some advice. Sure enough, she's seen the same torn-out-chunk problem resolved by our friend Jim Shaver. She said he just turned the blank down to the brass tube, careful not to cut into the brass, and squared up the end of the remaining wood. A new piece was drilled, and one end squared up with a pen mill (this is why you save all your teeny scraps of "interesting" wood!) and glued into place. After it dries, you square up the new end with the mill and go back to the lathe.
So off I went to see if I could make this work. The torn blank was quickly and easily fixed up, with a block of beech added onto the end. The skinny blank needed about half it's length turned down. This went OK, but when I was sanding the remaining CA glue off by hand the tube came loose and the rest of the wood slipped off. An Omen! Right, cut another piece of beech and replace the entire thing. So now I have a pen that's 3/4 beech, with a bit of curly maple left. Kinda looks like I patched a beech pen with maple instead of the other way 'round.
I put the blanks into the bench vice and used a chisel to make them roughly round (again). I'm all set for next weekend with the pole lathe now.
---- time passes slowly, oh so very slowly, through a short yet uninspiring work week --------
Canada Day found me out in the yard at the cottage with the pole lathe again. My son David was wielding the camera this time. He's 10, he knows a bit about light and focus, but in practical terms he just points and shoots anything that looks interesting to him. We got some really intereating shots to say the least... Anyways, I mounted one pen blank on the shortened mandrel and took a freshly honed gouge to it. This time, most of the kinks had been worked out and everything went reasonably well. A bit of candle wax in the depressions that take the dead centres makes everything run more smoothly.
I got the blanks turned down to meet the bushings, sanded to 400 grit, and then applied a friction polish. I suspect that a pole lathe is not the best means of doing a friction polish finish, as you don't get a whole lot of speed, but it worked!
I used one of those little clamp-on vises on the picnic table to press the pen parts together. We have 4 of these vises hanging around now. Seems I cannot turn them down when they're on sale at Canadian Tire for $9.99
And then, the moment of truth, does it work? Yes! Success!! I have made a pen on a pole lathe. It's not the prettiest pen I've ever made. Well, OK it's the UGLIEST pen I've made, but by gosh it's been the most fun!
Wood Hoarder, Blade Sharpener, and Occasional Tool User