Best valve design given that it is to be made of wood?

[Train_Fan]

Hi all,
For my next project I plan on making a straight 3 engine out of wood, using actual ball bearings that I have en masse and for operation off of pressure not volume.

My one roadblock is that I plan to make this as close to an auto engine as I can, and therefore intend to use camshafts and lifters for intake and exhaust, but I cannot feasibly implement rockers and normal "valves" at this time. So I have turned to you for some design input.

My idea is as follows, drawn up in my handy CAD program "Microsoft Paint":

Given higher-ish pressures of ~20psi and under, would this be the best design given the fact that would be made of maple/cherry?

Thanks much,
TF

 

[aarggh]

The first thing that comes to my mind is the contact points between the cam and the lifter are going to deteriorate very quickly! 20psi is a fair amount of power for a wooden engine.

cheers, Ian

 

[ShopShoe]

Could your design incorporate brass sheet cut and formed on the contact/wear areas. I have seen oak with brass used in this manner on old wooden devices. Unfortunately, I can't remember what and where the applications were. Brass sheet should be easy to cut and form.

Just an inspiration.

You're starting to make me want to make something mechanical out of wood.

Best of luck

--ShopShoe

 

[Train_Fan]

Good points on the pressures and wear.

I do not have brass sheet handy, but I do have copper sheet. Would that work?

 

[cidrontmg]

Forget copper, likewise aluminium. Brass is ok, bronze is better, and steel is best. Not even the best of woods would work with a cam+rod lifters, although Lignum vitae (or boxwood) can, in some structural works, even substitute metals (bearings, for example). Maple, oak, cherry - I don't think so...
What about plastics? ABS, Nylon, POM/Delrin, etc. Or Corian, Tufnol, Kevlar, PEEK, etc. Lots of stuff, can be very good for working without metals.

 

[Brian Rupnow]

Ah heck--Use wood if you must. Just use a round wooden wheel setting in a slot in the end of your pushrod to ride on the cam, and a slot thru the pushrod for a nail to hold the pushrod from revolving. For the valve, incorporate a rubber o-ring glued either to the valve face or inset into a pocket where the valve seats.

 

[Mike1]

Making your cams and pushrods from Maple which is a good close grained wood, you could soak the components in Raw Linseed Oil this will give them a nice wearing working surface, joiners who used Beech hand planes used this trick it made using the planes easier and the sole of the plane lasted longer.

Mike.

 

[Train_Fan]

Ah heck--Use wood if you must. Just use a round wooden wheel setting in a slot in the end of your pushrod to ride on the cam, and a slot thru the pushrod for a nail to hold the pushrod from revolving. For the valve, incorporate a rubber o-ring glued either to the valve face or inset into a pocket where the valve seats.

Haha, when woods all you've got its a must.

Hmm, So like those wheels on pinewood derby cars would suffice I suppose. No wood lathe so. I'll have to see how rubber wears against wood.

Making your cams and pushrods from Maple which is a good close grained wood, you could soak the components in Raw Linseed Oil this will give them a nice wearing working surface, joiners who used Beech hand planes used this trick it made using the planes easier and the sole of the plane lasted longer.

Mike.

Maple is whats intended for most of this, with cherry bearing surfaces as I have plenty of that and it wears well against wood.
While I can get raw, would boiled suffice in your opinion? (I am terrible when it comes to wood finishes.)

 

[Mike1]

Maple is whats intended for most of this, with cherry bearing surfaces as
I have plenty of that and it wears well against wood.
While I can get raw,
would boiled suffice in your opinion? (I am terrible when it comes to wood
finishes.)

Boiled linseed oil is more a surface finish, the Raw linseed will soak into the wood and won't affect your working clearance's.

Mike.

 

[Train_Fan]

Alright, thanks.

So, in the consensus so far is that this type valve would be best, if not at least functional?

 

[Septic]

Having used wood for many engineering applications I would recommend machining your valves and other bearing/friction surfaces well oversize and then charring them in a fire so that after finishing the fire-hardened surface is still thick enough to do the job... I would use maple personally as it machines and hardens better than cherry in my experience, but African Blackwood or lignum vitae are by far the best (just one look at a clarinet, old snooker/pool balls or a set of bowls will tell you why)

The reduction in friction, decreased porosity of the wood, hardened surfaces and closer machining tolerances will allow you to run the pistons "tighter" in the bores and with a sufficient flywheel mass you shouldn't need more than 10psi and would allow slower running with softer springs (less wear on cams/valves etc), but whatever pressure you use, you must make sure that the air is dry, or allow greater clearances to cope with any swelling.

I certainly would never oil any part of a valve, lifter, or cam lobe, because it tends to make the wood swell and become slightly spongy but cellulose dope applied very thinly in several coats may increase wear resistance at touching surfaces.

 

[Brian Rupnow]

The problem I see with your valve arrangement is that it will leak air badly around the sliding rod. If you truly want it to hold some compression, then run it like a conventional automobile engine. The difference of course, is that the underside of the valve (The face) would not be tapered like an automotive valve--it would be flat. In the area where the valve seat would normally be, put in a shallow counterbore slightly smaller than the diameter of the valve head and glue a BUNA-N (soft rubber) o-ring into the counterbore for the valve to seal against. The valve spring would normally hold the valve sealed against the o-ring with very little air leakage (if any), and the lifter would lift the valve for air admission.

 

[Brian Rupnow]

I wouldn't put any paint or varnish finish on the wood. That just makes it very "sticky" and more apt to bind. I have much better results with a good paste wax. It seals the wood, polishes off, and leaves the wood surface "slippery" as opposed to "sticky".--That's why skiers use wax on wooden skis instead of paint or varnish.

 

[Train_Fan]

Having used wood for many engineering applications I would recommend machining your valves and other bearing/friction surfaces well oversize and then charring them in a fire so that after finishing the fire-hardened surface is still thick enough to do the job... I would use maple personally as it machines and hardens better than cherry in my experience, but African Blackwood or lignum vitae are by far the best (just one look at a clarinet, old snooker/pool balls or a set of bowls will tell you why)

The reduction in friction, decreased porosity of the wood, hardened surfaces and closer machining tolerances will allow you to run the pistons "tighter" in the bores and with a sufficient flywheel mass you shouldn't need more than 10psi and would allow slower running with softer springs (less wear on cams/valves etc), but whatever pressure you use, you must make sure that the air is dry, or allow greater clearances to cope with any swelling.

I certainly would never oil any part of a valve, lifter, or cam lobe, because it tends to make the wood swell and become slightly spongy but cellulose dope applied very thinly in several coats may increase wear resistance at touching surfaces.

Alright. Its kind of hard to machine wood to these tolerances without a lathe, and well, wood swelling would make that very hard to achieve. The pistons themselves are probably going to be 1/16th undersize and use 2-3 O-rings or similar to both seal and center the piston in the bore.

As for oils, I have not found much swelling when using mineral oil as a lubricant/finish on other projects. Though while fire-hardening is a good angle, I would like to try the copper facing first as it is available. For me material (wood) is free so I have room to mess with things like this. I shall experiment when it comes to it though, so thanks!

The problem I see with your valve arrangement is that it will leak air badly around the sliding rod. If you truly want it to hold some compression, then run it like a conventional automobile engine. The difference of course, is that the underside of the valve (The face) would not be tapered like an automotive valve--it would be flat. In the area where the valve seat would normally be, put in a shallow counterbore slightly smaller than the diameter of the valve head and glue a BUNA-N (soft rubber) o-ring into the counterbore for the valve to seal against. The valve spring would normally hold the valve sealed against the o-ring with very little air leakage (if any), and the lifter would lift the valve for air admission.

Good points, and I did not consider that angle for the valves.
Though where would you suggest ordering the O-rings and valve springs from?

I wouldn't put any paint or varnish finish on the wood. That just makes it very "sticky" and more apt to bind. I have much better results with a good paste wax. It seals the wood, polishes off, and leaves the wood surface "slippery" as opposed to "sticky".--That's why skiers use wax on wooden skis instead of paint or varnish.

For this I would be using Mineral Oil, Linseed oil or something similar for the main finish. I will definitely keep the paste wax in mind though!

 

[ShopShoe]

Didn't think to mention Paste Wax. I have used that on wood projects and surfaces for years: It's a standard shop supply for me and right next to the WD-40 in versatility. I think it will help your engine run very well.

--ShopShoe

 

[Brian Rupnow]

Pretty well any nut and bolt supply store such as "Fastenall' will have a selection of different compression springs and rubber O-rings.---Brian