acme thread for large wood screw

nicely

Hello Bob, you are cutting the male thread? I have heard [not seen] of it being done, using a Dremel with the appropiate shaped cutter burr,mounted on the toolpost and cutting at whatever t/p/i needed. Worth a try? All the best for now, John.

Perhaps do a search on wooden screws ("wood screw" makes me think of a screw to go into wood) -- anything that's easy to split won't make good threads, because you're asking them to hold along the grain, where the wood is very weak. I think you're right in trying different woods, but you haven't looked far enough afield to find the right one.

I'd try Elm. Elm was used for wheel hubs because it has a dense interlocking grain -- apparently it was a bitch to work with because you simply could not split out blanks but had to saw everything. Assuming the grain is fine enough that should be just what you want for this part.

Obligatory disclaimer: I haven't actually done this; I've just watched a lot of episodes of "the woodwright's shop" and read a couple of Roy Underhill's books.

nicely

Oak is probably going to be a non-starter. You need a close-grained, tough wood, like hickory, maple or ash. They make threadboxes for doing the male threads, the thread isn't much like a metal thread. Several woodworking books I've seen tell you to shape the threadbox cutters and make the threadbox itself. Or you can go to some of the specialty places on the internet and buy them and the matching taps. I've used threadboxes on

Go to a firewood pile and select whatever species of wood is common to your area that is a pain in the ass to split with a maul. If the cutting tool is not razor sharp with no rounding of the edge forget turning it with no tearout. Dampening the wood with a moist but not dripping sponge may help.

Try

Seems to me that using a wooden screw for a vise is something you would do if metal were not available. The only time I have seen wooden threads is on broom handles painting poles and that is the usual point of failure.

"Seems to me that using a wooden screw for a vise is something yo would do if metal were not available. The only time I have seen wooden thread is on broom handles painting poles and that is the usual point of failure."

I've seen such threads on "decorative" nut crackers. It's a wooden cup roughly the size of a coffee cup, for the nut, and a wooden threaded ra for cracking the nut.

Can't help with the wood type however

-- J. Mark Wolf

|| ||Roger Shoaf wrote: || ||"Seems to me that using a wooden screw for a vise is something you ||would do ||if metal were not available. The only time I have seen wooden threads ||is on ||broom handles painting poles and that is the usual point of failure." || || || ||I've seen such threads on "decorative" nut crackers. It's a wooden cup, ||roughly the size of a coffee cup, for the nut, and a wooden threaded ram ||for cracking the nut.

I have a 3-legged stool with adjustable height via a large wooden acme thread. Blonde finish, almost looks like pine. Whole thing cost me $10 new, so it couldn't be anything exotic. Texas Parts Guy

I find it very difficult to single point a wood "screw".

What does work well is to mount a router on the toolpost and user that to cut the threads. A 60% v bit in the router, and a slow back gear works well. If you want some other tread form then the proper router bit may be harder to find.

S> Try

Cheat; use plywood. Or even metal (plastic) painted with wood grain ;)

I'd try Maple, or one of the various IRON woods (every state and country has one!). Purple Heart might be ok - it is hard.

Cell size and material composite is important. A little Si in the wood helps but will eat the cutters - use carbide or regrind.

Martin

"bob" wrote: (clip) Anyone with experience doing this? (clip) ^^^^^^^^^^^^ I am a woodturner, not a machinist, so I will tell you what little I know:

1.) You can sometimes help with tearout by waxing the wood, treating it with lacquer sanding sealer, or thin C/A glue. 2.) You need to use very sharp tools. 3.) Woodturning practice is to turn the wood fast to get better surface finish. I don't think this is applicable to turning threads in a metal lathe. So the suggestion to use a router mounted on the carriage would likely be the best way to go. There are woodturning tools designed to work this way--it seems to me that a machine lathe would do this easily.

A look at a wood working web site that has thread cutting hand tools might help in the physical cutter and angles. e.g. a wood working supplier...

Martin

I made the mistake of trying to split some elm for firewood once. Karl

One of the Tauton books has a couple of articles from Fine Woodworking on making a screw box to cut screws out of wood. Unfortunately I can't find the exact reference.

IIRC the design of the screw box was pretty simple.

--RC Projects expand to fill the clamps available -- plus 20 percent

If you're using a form tool--a cutter shaped exactly like the profile you are cutting away--then you likely have zero rake on the top of the cutter, and you are just scraping instead of slicing as wood likes to be cut. That may be OK with maple or other woods of similar hardness if you take light cuts for each pass. But if you're trying to hog a lot of wood in one pass, the result will be chipping and tearing, especially in oak.

If you were to slice the wood instead of scraping it, the cutting edge needs to be keener, or have much less of an included angle between the front or side of a toolbit and it's top face. Only way to do this is to have a seperate cutter for each flank (right and left, plus the root)--unless you are skilled enough to grind a cutter tip with positive backrake on all three edges (not very easy).

So you're back to the flat-topped cutter, taking several light cuts, or a rotary cutter in a router which I would recommend. Elm or maple are much better choices for wood, as others say.

Ken Grunke

If you look at the cutters in a typical wooden screwbox, you'll find that their geometry is quite a bit different from that of the cutting edge of a tap.

A woodworking tap presents the cutting edge to the wood in essentially a scraping orientation. There may be a slight amount of rake, or there may not.

A screwbox uses a V shaped cutter, presented to the work on a tangent. Think of a wood carver's V tool - V on the outside, V on the inside, with the edge razor sharp. Or, a piece of angle iron with the end cut at, say, 60 degrees (with the points longer than the heel), and the inside edges then sharpened. Again, the cutter does not scrape, but is presented to the work pretty much at a tangent - and it slices. It produces not chips but a continuous curl. A larger screwbox will usually have two cutters, so you will want to make several passes on the lathe.

John Martin

Hydraulic only!! Ever see a 24 ton splitting ram come down on a 16" block of straight grain elm, bury itself in a couple inches, and STOP? Sheesh! Had to use a sledge hammer to get the ram out of the log.

The new sapwood for each year grows > I made the mistake of trying to split some elm for firewood once. > Karl