Threading a piece if laminated wood

[Ian PParticipant @ianp]

Can I be the first to ask,

What is that device Bernard?

Ian P

[bernard towersParticipant @bernardtowers37738]

Its a lock stitch needle for leather work, this is it with the cover off

[Ian PParticipant @ianp]

I will Google it (i dont see a needle) and the image 3768 just shows as a place holder, seems a random feature of the forum.

Ian P

[Ian P]

On Ian P Said:

I will Google it (i dont see a needle) and the image 3768 just shows as a place holder, seems a random feature of the forum.

Ian P

Update….

The image has now appeared instead of just the placeholder.

I seem to remember that a while ago someone mentioned  images appear after a delay.

Ian P

[Neil LickfoldParticipant @neillickfold44316]

The very thin cyno works well for hardening the wood for cutting wood threads, internal and external. The live tooling is the best option I have found. I use an old metal, Dremel handpiece that is parallel in a holder on the toolpost. I have the topslide at 60deg and feed in like cutting a metal thread and feed in on the flank angle. It reduces the load on the Dremel tool. For deeper threads like the 3/8-10 used in pool cues, I cut 2/3 of the thread depth, then re apply the thin cyano into the threaded area. Leave it to dry for 20 mins or so and then carry on threading. With a 1.5mm pitch thread, it can al be done in 1 pass if the thin cyno has penetrated deep enough.

I used to make carbon fibre pool cues and undertook cue repairs, until I discovered allergies to the Rose woods used in cues.

Neil

[PeteParticipant @pete41194]

It isn’t uncommon to use threaded wooden parts in Ornamental Turning. But there almost always using extremely dense and hard wood. And in general, the thread pitches they would normally chose would be much coarser pitched than what your wanting. I just don’t see finer pitched wooden threads like that being durable enough even when hardened with the the super glue. Not with the guessed at working forces that tool might see during it’s use. A properly threaded steel or brass insert permanently expoxied into the wooden handle would be the route I think I’d chose. The wood type, the fine pitch thread and the weaker cross grain wood structure the threads are being cut on are all working against you.

[gerry maddenParticipant @gerrymadden53711]

I often hesitate to be completely open about the purposes of some of my activities in order to avoid receiving dozens of replies advising me not to do it and to leave such things to the “experts”. Quite funnily though, in this particular case the debate got there on its own! The application is a propeller blade. Whilst there is plenty of interesting and clever prior art on the subject, (which can provide some guidance) my personal challenge is to make use of existing wooden blades and install them into a new design hub unit. What I am doing at present is experimenting to find the best ways to attach a steel cup to wood, using dummy representative parts. A key requirement here is that I must be able to process the parts myself without too much outlay on special tooling/equipment.

The above point was one of the reasons I selected a 1.5mm thread. I thought it might be ‘do-able’ with a single point cutting tip. The other is that I cannot really reduce the diameter of the existing blade roots by more than 1.5×2 mm. So bigger (deeper) threads are not an option.

As for the wood, at the time I believed the existing blades laminated in Beech. Now I find out that they are likely to be Rock Maple. This may be better for cutting. However, if I continue with the thread idea, a high-speed router cutting tip or wheel is probably the sensible way to form it.

The suggestions of using super-glues to harden the wood prior to cutting are great ideas. The negative of this though is that I would probably have to demonstrate to the authorities that super-glue has no long-term reaction with the lamination glue in the existing propeller roots. This would not be beyond the wit of man but would of course take more time and money. The less ‘new’ I do, the less the authorities can quibble about.

To bring you up to date, despite my dreadful threading of the laminated wood I proceeded to bond them together anyway.  When the glue had cured I made a strength test. The joint and achieved a load of 6.5 tons before failure which was more than I expected. The failure has occurred in the wood (by shear) with no signs of thread remaining. This makes me wonder if threading (at least with such fine pitch) is really a source of weakness. Perhaps a plain or dimpled finish might be stronger? This is likely to be my next trial.

Gerry

[bernard towersParticipant @bernardtowers37738]

Gerry your threaded glue line will be stronger by virtue of the fact that it is longer.

[gerry madden]

On gerry madden Said:

[…] What I am doing at present is experimenting to find the best ways to attach a steel cup to wood, using dummy representative parts. A key requirement here is that I must be able to process the parts myself without too much outlay on special tooling/equipment.

[…] This makes me wonder if threading (at least with such fine pitch) is really a source of weakness. Perhaps a plain or dimpled finish might be stronger? This is likely to be my next trial.

Gerry

.

Trust my opinion, or not, Gerry … entirely as you wish.

I think your best option would be to use one of the Loctite anaerobic retainers.

The way they work is entirely suitable for a use on a close sliding fit twixt wood and steel.

MichaelG.

[Mark EasingwoodParticipant @markeasingwood33578]

This may or may not be of help.

Last week I took the top off a woodworkers die box, and the cutter is, as I suspected, shaped like a woodcarvers vee tool. The Taps appear to be a 55 degree thread form.

 

In the spirit of curiosity, experimentation and adventure I removed the cutter, and clamped it in the tool post, as high as I could get it. (The cutting angle in the die box is towards the outer diameter of the wooden blank, similar to a woodturner using a chisel or gouge).

I then found a piece of Kiln Dried Beech, which has probably been in the workshop for a decade or two, so it is probably too dry for this purpose, air dried timber would cut better I think. The cutter could be sharper too!

The 9 TPI thread is not too bad, but the 18 TPI thread is very poor. Cut slightly too deep and the thread crumbles to dust.

My conclusion is that it should be possible to file up a cutter in silver steel, and cut a thread, so long as the timber is suitable, and the thread pitch not too fine.

Mark.

[Neil LickfoldParticipant @neillickfold44316]

Gerry, Before live tooling for pool cues, they used compression dies. The new thread form is a radial thread. The tool has a R1.5mm radius top and bottom of the threads.

When cutting with a fixed form tool like in metal thread cutting, the fibres are damaged from the process, so it will not be as strong.

I think coach bolts are 10tpi or so.  Remember to make the thread a little loose, so that you can get plenty of glue between the two parts. As the glue soaks into the wood, it will become stronger as well.

Neil

[gerry maddenParticipant @gerrymadden53711]

Nick – interestingly I had considered rolling a thread but I wasn’t aware of such being done in wood before so good to hear your experience. Many prop blades in the past had compressed wood in the root section. The compression, (provided it doesn’t break the fibres), increases the density and therefore the strength. I will think about this possibility.

Mark – Unfortunately I can’t really increase the thread size but I’m sure a big one would be easier to cut.

Michael – Unfortunately I will probably be restricted to one of two wood glues approved for aviation/wooden prop use. These are probably not the best adhesives in the world these days as they have been around since the 50’s. But to get approval for anything else would involve a huge amount of work and cost. Initial strength is not the only issue – it’s an ageing and compatibility thing. I would have to prove that the alternative proposal could withstand tens of years of temperature and humidity cycling, UV, ozone, approved paints, oils and fuels etc. Life would get far too complicated :).

Gerry

 

[gerry madden]

On gerry madden Said:

[…] Michael – Unfortunately I will probably be restricted to one of two wood glues approved for aviation/wooden prop use. These are probably not the best adhesives in the world these days as they have been around since the 50’s. But to get approval for anything else would involve a huge amount of work and cost. Initial strength is not the only issue – it’s an ageing and compatibility thing. I would have to prove that the alternative proposal could withstand tens of years of temperature and humidity cycling, UV, ozone, approved paints, oils and fuels etc. Life would get far too complicated :).

Understood, Gerry

… I wish you success, whatever method you settle on.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

As this is for a wooden aircraft propeller, Gerry is working on a problem that must have worried dirigible pioneers when the Wright brothers were little boys.

All early propeller blades were made of wood fixed into a metal hub.    As propellers rotate at high rpm the centripetal force pulling them out of the hub is substantial.  At the same time the blades are pulling the mass of the aircraft at a right angle behind them.   Mechanically stressful, often flying in the wet and it’s very bad news if a blade comes off!

Bet blade fixing has been researched up the Ying-Yang and beyond by generations of aeronautical engineers.  All we have to do is find out how it was done in the past – maybe Gerry already knows   I’ve got a 5 volume set on aero-engineering circa 1930;  pretty sure it doesn’t cover this but I’ll make sure.   Should blades be pinned as well as glued? I’ve no idea.

Super project!

Dave

 

[Alan CharlestonParticipant @alancharleston78882]

Hi,

I came across this video on Y.T.

Very interesting. He’s cutting a very coarse thread and powers the lead screw to drive the chuck instead of vice versa.

He cuts the thread using a router.

Regards,

Alan C.

[gerry maddenParticipant @gerrymadden53711]

Nice video Alan, thanks for showing it.

I did notice though that he still managed to get quite a few chips and breaks on the crest of the thread i.e the weakest part. Since I am very limited in the depth of thread that I can use, it makes me wonder whether even a high-speed cutter would be able to do a good-looking job.

I’m also now questioning whether the shear strength of the glue is probably higher than the shear strength of a thread in wood and therefore what am I gaining from threading it? It might be better to consider other methods of making the joint.

Gerry

 

[FulmenParticipant @fulmen]

My first thought is to consider “prior art”. If it’s a known and previously approved method you will have less problems getting it approved.

[gerry madden]

On gerry madden Said:

[…] I’m also now questioning whether the shear strength of the glue is probably higher than the shear strength of a thread in wood and therefore what am I gaining from threading it? It might be better to consider other methods of making the joint.

Exactly, Gerry

That’s what I was trying to suggest earlier, when I  mentioned anaerobic retainers

MichaelG.

[Neil LickfoldParticipant @neillickfold44316]

Originally , they may well have used compression dies to form the thread into the wood. The inside of the tread for the die is radiused like w Whitworth form but have quite a generous radius. The tool or tap that cuts the Ferrule or in your case the metal cap, has a matching large radius tool but is effectively a truncated thread form. You may be able to find some data on the original way that they were attached. The compression dies do not create threads that are as deep as metal threads for the same pitch. Neither are they as sharp on the root radius.

You will need to make the tool to create a compression die, and have a 10 to 15 deg lead in taper to the die.

Neil

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