Motor mount wood??

I recently picked up a piece of wood to cut into motor barriers. Thought it was maple, but it turned out to be alder. Nice grain, but some pieces warped when I ripped them into 3/8 by 1/2 strips. I still ended up with several good pieces. Any opinions on using alder, birch, or other woods in place of maple???

I've used white oak for engine bearers on a handful of SLC planes... just because I didn't expect them to last that long. Still have 3 of them after 2 years and they're as good as new. I'm suprised, to say the least. I bought the wood from Home Depot but I only got the oak because they didn't carry maple. Honestly, if I were building something that I expected to be around for more than a season, I'd go with the maple, it's just not that expensive.

Hi

Your woods are different from ours in Aus. Maple here is Martanti or Pacific Maple and is a very easily split softwood, about the last thing I'd use for engine bearers. I'd look for dense timber that is difficult to split. Don't care what it is as long as it's not easily split and dense enough to resist bruseing from the engine mount flange. Look for a cross grain like oak or a wriggly or interwoven grain, not a straight regular grain.

Last thing I used was spotted gum and that worked well.

I always rip oversized because internal stress from fast curing can cause the timber to warp or curve when ripped.

An interesting question....

Each wood has certain characteristics that suit specific applications. First, they need to be commercially available, or else you need to be a forester! Believe it or not, there is an "industry" here in Los Angeles that tries to make use of trees harvested from people's front yards.... It is the only way to get some exotic species.

While maple has been the hardwood of choice for model airplane motor mounts it certainly isn't the only wood that can work. I would rank the readily available (here in LA) woods as follows: hard maple, yellow birch, then way down the list, red oak, and red alder. I would rank white oak well above red oak, but you're not going to find it unless you go to a really good lumber yard. This comes from the northeast, and we don't get much out here. Apparently, it has suffered from over-harvesting. I don't like working with oak because it is ring porous, and tends to chip and split when you are working with small pieces. (The motor mounts in my Noblarf look like oak or ash, but may be an asian species? They had already fuel-proofed them with epoxy so it is even harder to tell.) Maple is diffuse porous and working it is a lot like machining aluminum. So is birch. I have found red alder to be more like mahogany. Kind of splintery, but doesn't split like oak. There are plenty of tropical woods that are even harder and stiffer than those mentioned but they weigh more too. Some are toxic and give people allergic reactions.

And wood varies a lot so it isn't like comparing brass, steel and aluminum. Ask how many guys know where they grow 4 lb balsa trees! So you have to start with a good piece, from a suitable species.

I consider the important selection criteria to be:
1. Density (Maple=.021 lb/in3; R Alder=.015; Y Birch=.022; W Oak=.025)
2. Modulus of Elasticity (Maple=1.62E6 lb/in2; R Alder=1.38E6; Y Birch=2.01E6; W Oak=1.78E6)
3. Hardness (Maple=1180lb; R Alder=590; Y Birch=1260; W Oak=1210)
4. Compression Strength,cross-grain (Maple=1020 lb/in2; R Alder=440; Y Birch=970; W Oak=1070)

You can divide (2) by (1) and use specific stiffness as your criteria. Alder ranks high here; a little higher than birch, a lot higher than maple. The problem with alder is that the hardness is half that of maple or birch. If you don't like how your blind nuts or flat washers sink into maple, you're not going to like alder at all. And I don't like splinters, either.

As far as warping, be sure to start with a straight board. No bowing, no cupping. (Don't worry too much about crook.) Then look for close, straight grain. Avoid boards with weathering and checking. If the boards are S2S, some guys can tell if they have wind shakes. I just go for it! Be sure you use kiln dried wood with a low moisture content. Woods that have high radial shrinkage relative to their tangential shrinkage generally warp pretty badly. That data is available for most species.

If you're still not bored by talking about hardwoods (balsa is techically a hardwood!) you can access lots more info from the industry standard reference: Forest Products Lab Book. You can see most of it on-line if you search under "properties of wood."

Way too much fun!

Dave
LA_Flyer

PS-I'd use a good piece of birch anytime.... On my current plane, I replaced the kit maple bearers with a one-piece maple construction with lots of holes drilled in it. Unfortunately, since I was in a hurry, I had to cut from a really nice board with curly maple grain....

Dave,

Since you seem to be a "wood expert", I'll drop in a couple of names you probably don't know:

Jacarandá...and..Massaranduba

Jacarandá is a very expensive red-brownish wood used for making furniture.
A jacarandá table can cost a small fortune. But, some buddy of mine gave me a pair of mounts made out off this stuff, they are really good.

Massaranduba is suposed to be the hardest wood around. It's nicnknamed "Pau de dar em doido" (wood to whack crazy people with). It's very dense, but it will outlast your plane and engine.

Awwww, c'mon Ion, that's too easy!

The common (local) name for jacaranda is Brazilian rosewood (Dalbergia nigra). Every woodworker, furniture maker, instrument maker, etc. just drools over the possibility that he will stumble across a stash of the stuff someday. (If you have any, let's talk!) The problem is that it is now endangered, is on the CITE list, and should no longer be harvested unless we are talking about sustainable, plantation grown wood. Since there are so many other good woods for engine mounts, it would be a crime to use rosewood! (But if you insist, wipe it with acetone several times and then glue it with epoxy.)

As far as massaranduba (Manilkara bidentata), I have never workesd with it. I have only seen a collectors coupon. From the listed properties, it should make a very pretty, though heavy motor mount.

Roy,

I've used a lot of stuff. Poplar, alder, and a ton of exotic woods (I had scraps around). As long as it's protected, I think you can use pretty soft woods and alder is pretty soft. An aluminum pad underneath should help.

Best I used was some stuff called colinga. I tight grained hardwood that's not oily or brittle. Carves well too. I had some scraps from a local hardwood place.

Roy,

Although "Bird's eye" Maple has been the wood of choice for many years. There are many other woods that will satisfy our requirements. I've spent most of my life in the cabinet and trim business and as a result have at least a layman's knowledge of different woods. It also depends on whether you're strapping down a howling .15 or a super zoot .65.

What we are looking for is a hard, tight/closed grain wood. One also needs to be aware that all pieces of wood are not created equal. As in 4# balsa is not the same as 12# balsa all maple is not the same and some maple is not suitable for our applications.

Availability is another problem as someone mentioned in another post. White Oak is easily obtained in Missouri, OK, AR, East TX but is probably hard to come by in CA. (I don't know)

Not trying to start a fight here but here are woods that in my opinion would work well and may be available at good lumber yards that cater to cabinet makers.

Maple: 1st on my list because of tradition and besides, I have some.

Cherry: Very hard and tight grained
Cedar: Aromatic variety as in Cedar chest. Not the fence material.
White Oak: Good but watch the grain
American Black Walnut: Lots of different walnuts "burled" is fine but some is soft.
Basswood: Hard to find but works very well. 40s-50s modelers used this a lot.
Birch: Good, watch the grain

All woods need to be properly dried/seasoned/aged. "Green" will give you problems whatever you're doing with it. Hope this helps.

John,

I agree with most of your comments. I remain a "sometimes" amateur furniture maker. Building and flying CL has really cut into that hobby! I admire those who are able to make a living working wood....

White oak is hard to come by on the west coast. The last ten years or so, you'd think the only hardwood left in America is red oak. I think it is to the point that availability is now dictating furniture style.

I'm surprised that you included basswood and incense cedar on your list. Basswood is really soft and has low compression strength relative to the other choices. Cedar is only slightly better. I have also had difficulties finding (at least here on the west coast) straight grain cedar in decent sizes. The cedar I have worked with has also had brittleness and cracking issues. Mebbe they're keeping all the good stuff in Arkansas? Mebbe they're cutting it all up into that thin paneling for your closet? I would rank poplar above both of these for motor mounts, and I don't like poplar....

I'd use a good piece of black walnut in a minute, and would consider cherry. And I agree with your sentiment to use "...what I've got." (I still can't imagine Brazilian Rosewood mounts, though.... Sell it to a pen maker and pay for a good used engine!)

I added data for comparing the latest woods mentioned:

1. Density (B Walnut=.020 lb/in3; Cherry=.019; Cedar=.013; Basswood=.014; Balsa=.006)
2. Modulus of Elasticity (B Walnut=1.68E6 lb/in2; Cherry=1.49E6; Cedar=1.04E6; Basswood=1.46E6; Balsa=.49E6)
3. Hardness (B Walnut=1010 lb; Cherry=950; Cedar=470; Basswood=410; Balsa=N/A test not valid)
4. Compression Strength,cross-grain (B Walnut=1010 lb/in2; Cherry=690; Cedar=590; Basswood=370; Balsa=300)

As far as "birdseye" maple being the standard for motor mounts, I think the standard species is sugar maple or black maple (acer nigrum). As a cabinet maker, you no doubt know that birdseye is a colloquial name for wood grain with a large number of undeveloped(?) eyes. But from the same tree you might get curly maple, fiddleback maple, flame maple or burled maple depending on how it grew and where you cut it from the tree. (The last I heard, the wood technologists still don't know for sure what causes birdseye figure.) A few years back, a friend of mine got together with a couple more guys and bought a whole semi-truck load of maple. Trucked it to LA all the way from the northeast somewheres. A couple of the guys wanted it for commercial flooring, so they took all the clear, straight grained stuff. That meant my friend had to take the birdseye and curly grain wood for his furniture jobs. Of course, he was broken up over that!

I'd rank the indigenous woods mentioned for motor mounts as follows:

Maple (Ok, I'm a traditionalist. As proof, I own two Fox .35's)
Birch (Great stuff! I used it for the endcaps and vise jaws on my cabinet maker's bench)
Black Walnut (Good stuff, but would be harder to see damage or cracks. Highly recommended for those who don't crash but are contrarians)
Ash (Ring porous, but I like it better than oak. Good enough for baseball bats....)
Cherry (Great for furniture, but somehow just seems wrong to use in airplanes. Requires mahogany stain for maximum appearance points)
White Oak (If you have it, and you don't have anything above on this list. Extra zoot points if you convert to bog oak using ebonizer)
Poplar (If you have it, don't have anything above, AND its a pukey profile with an OS Max)
Red Oak (Go to LHS and buy maple; else stop building CL and finish the dang accent tables for the living room)
Red Alder (Go to LHS and buy maple. If they are out, get sterile needle ready to pick out splinters)
Douglas Fir (If tight grain and old growth, reposition mounts so you can use aluminum pads and still have spinner line up)
Cedar (Quit stunt entirely and build hope chests and shoe trees. Get rich; only buy Umland kits with rock maple mounts thereafter)
Basswood (Brag to Pro-Stunt buddies about clever weight strategies. Don't tell stunt buddies why you installed steel cable between engine case and bellcrank. Position flight box and car appropriately)
Balsa (Use only the 14 lb "junk." Install Norvel .061 in your 54" microlight stunter. Pray to wind gods regularly)

In my current plane, I have Baltic birch plywood fuselage doublers (5-ply), sugar maple motor mounts, a douglas fir wing spar, and the balance is our favorite hardwood -- balsa!

Dave
LA_Flyer

PS-If you're on a budget and gotta go exotic, check out the "microwoods" available from Woodworkers Source.

Dave,

Going off topic here but a great story:

I lived in the Missouri Ozarks for 10 years and a large part of the economy is forestry. Black Walnut, Cherry, White and Red Oak, Cedar, White Pine, Hickory are the most abundant at prices no one would believe. Example: 5 quarter S2S Black walnut at 1.65 per BF. White Oak, 1.35, Cherry, 1.85, White Pine 1.05. These prices aren't from the "good ol' days". They were current last year when I bought 400 feet of White Oak for some home projects. On to the story:

A Chicago retiree moved to the Ozarks and bought 40 acres. Built a nice home. Wanted to clear about 20 acres for a pasture and it was mostly Black Walnut. Sold the Black Walnut for a good deal of money but was left with the stumps in the pasture. He made a deal with another individual to remove the stumps for $50.00 apiece. The "Hillbilly" he made the deal with for stump removal knew that the prize wood for making gun stocks comes from the roots of large Walnut trees. (You're ahead of me aren't you). Mr. Hillbilly got paid for removing the stumps and made an additional $200 bucks each when he sold the wood from the stumps. Which brings me to comment on the only bumper sticker that has ever been attached to any vehicle I have owned.

"If you think education is expensive, try ignorance"

John,

Great story! At those prices I may have to drive back there with a trailer and stock up on materials. You mentioned hickory. Practically impossible to find in stock here in LA but I bet would be quite good for motor mounts. Is pecan similar?

So now that you have told your stump story, let me ask you how someone could dig one up and make a profit on it? Seems like a huge amount of work. Did he dig down and blast 'em out? I heard of one old-timer teaching a kid how to do this. They drove their pickup into the field, unloaded the stick, caps, etc. The old-timer went thru the process in detail to be sure the safety issues were covered. The blast lifted the stump out of the ground and it landed squarely in the bed of the truck. The kid then innocently asked "how do you know which stumps are too big to fit in the truck?"

Every time I see the term "white oak" I cringe. When I was in St. Louis, I was a MATCO tool dealer and our tool boxes were shipped from up state New York on white oak pallets. I gave them to a guy that made furniture as a hobby or burned them in my fire place. It doesn't coat the flues and leaves a nice fine white ash. Lots of heat. And now I find I could have ripped them for motor mounts. Five years of pallets, gone. sob!

I have a set of plans that shows a piece of plywood glued to each side of the hard wood. This gave me and idea. I glued several strips of plywood together and used it in place of my hard wood.

Hi Roy

I have used Cherry with very good results.
Every bit as good as Maple.

Hi Guys Wow, some really nice answers. I appreciate your time to respond. I am breaking down my computer and heading back to Washington state in the morning. Arizona is getting to hot for me!! I look forward to checking this thread when I get home and get the computer running again. Cheers, Roy D.

Speaking of motor mount material...goto a local cabinet shop and ask to dig through their scap wood. Most of their wood comes s2s straight line ripped to random widths. They'll have TONS of scraps (considered industrial waste by them) that make fine motor mounts.

I was just offered (literally) a DUMP TRUCK full of this stuff from a local lumber yard. Thinking about taking him up on the deal to fire my wood burning stove next winter. Would be enough to make 10,000 motor mounts AND keep me heated.

Maple, Alder, Oak, Poplar (probably not the best) are very common. Will find some other domestics.

I've personally used Cherry, White and Red Oak, Hickory, hard Maple, Walnut and Ash, all with no ill effects. Cedar Elm, Apple, Pear, Persimmon, really any fruit tree would all work well and are available from front yards everywhere. If you want to use it, cut it however you can to about 1" or less thick and let it cure for a year or so in a closet in your house. Should be just fine. DON'T try to use wood that grew anything other than straight up. Although the stuff from limbs looks good, you've never seen warpage and such till you try to play with that stuff. It's called reaction wood, and for a good reason! Even trees that grow crooked are useless for LENGTHS of wood. If you're making cubes, or turning blanks, you might stand a chance, but probably not motor mounts that you want straight.

Tools

Tom Morris told me he uses Spruce! I hope it is harder than the spruce I've used for spars in free flight planes.