Monthly Archive for December, 2010

Don’t trust anybody!

Published on December 29, 2010 in Machines. 4 Comments Tags: .

All right, that’s harsh. But sometimes we blame ourselves for bad results when the fault lies with equipment we just assumed was fine.

I’ve been working with my home made rose engine lathe, learning what it can do. Rose engines (more about them in the future) are slow at removing wood, so I hand-turn blanks to roughly the right shape on my traditional lathe, then use the rose engine for final shaping. To get the best possible registration as I move work from one lathe to the other, I got a Beall Collet Chuck to hold the blanks. Collets are more precise than scroll chucks.

Or, are they?

I chucked a walnut rod into the Collet Chuck and turned it round, then moved it to the rose engine. There was .007″ of runout! What’s up with that?

I know, 7/1000 of an inch doesn’t sound like much. In fact, noted turner John Jordan once told me that runout like that makes no difference at all. But I’m using the rose engine to cut through walnut walls only .014″ thick, to reveal white maple inside. It’s an sgraffito technique (where you cut through one surface to show a surface beneath). .007″ is half the wall thickness, and quite noticeable indeed. The pattern was obviously wider and deeper on one side of the piece than the other.

A collet chuck with runout problems

Time for some detective work.

I first assumed I must have turned the piece carelessly. So, just to be sure, I put the Collet Chuck back on the lathe and chucked a piece of 1/4″ drill rod in it. When I measured the runout with a dial indicator, it was .007″. You can see the setup at the left.

Here's the problem!

I took the Collet Chuck apart and looked at the pieces. These chucks have precision spring collets, held in a tapered hole by a screw-on cap that forces the collets to move into the body and tighten up, rather like router collets. When I turned over that cap, here’s what I saw.

The collet cap in my hand has a tapered opening that bears on the collet, forcing it into the hole. But this cap must have been machined near quitting time on Friday afternoon. Note how there’s a ridge of metal just inside the rear hole, and it’s off center! That meant the collet would be pressed into the chuck body only on one side of the top, virtually guaranteeing it would seat off-center.

Isn’t that often the way it goes? Halfway into a project, we have to stop and repair the machine or build the fixture to make the next step possible. Coming up next, fixing the problem.

Time for some alcohol

Published on December 23, 2010 in Finishing. 8 Comments Tags: .

Posting’s been slow of late—not because of alcohol, but from a combination of the usual holiday madness and the labors in launching a start-up company. But presents are wrapped, the PowerPoint file is saved, and I have a few minutes to tell about an interesting finishing solvent. (BTW, I’m just a satisfied user. I have no connection to the company.) I used this on the leaf plate mentioned in the last few posts.

White lightning shellac solvent

Tools for Working Wood’s wholesale division, Brooklyn Tool and Craft (BT&C), recently introduced a shellac solvent that’s 99.5% ethanol (drinking alcohol), with a little bit of rubber solvent as a denaturant.

So what, you say? Well, if you’re a fan of shellac finishes (as I am), you’ve probably used hardware store “denatured alcohol” to thin your shellac or dissolve the flakes; typically Kleen Strip’s S-L-X brand. However, BT&C’s product, while admittedly harder to find, has some advantages.

First, there’s safety. Read both Material Safety Data Sheets (MSDS). Of course ethanol has its hazards, but they’re more to do with inebriation than casual exposure. Observe the cautions on the label and MSDS, but it’s a pretty safe solvent. S-L-K’s Denatured Alcohol, on the other hand, is 50%–55% methanol, a more dangerous alcohol which can cause severe central nervous system reactions, according to its MSDS. BT&C’s shellac also has a flash point about 12 ºF higher than S-L-K’s, giving a little more explosion safety.

Second, there’s a usage advantage. I used BT&C’s alcohol to dilute shellac both for spraying and French polishing. Confirming what the manufacturer claims, my coats seemed to dry harder and faster than the same shellac thinned with the S-L-K product.

You won’t find this stuff in most hardware stores. However, it’s available on line at www.toolsforworkingwood.com, and also at Woodcraft stores. Give it a try and see what you think.