Which Wood Is Most Suitable?

[thkoutsidthebox]

Hi all,

I'm almost ready to post a thread about my next router. I've already sent e-mails looking for ballscrew quotes.

Anyway, staying on topic.....Im building it from hardwood. Without getting too distracted by the benefits or otherwise of hardwood, can someone please tell me the best hardwood to use for a cnc wood router considering the forces involved?

My previous softwood/mdf build was just not solid enough. Im sure the grain structure of the different woods can have a major effect on the end result. Would a close grained wood be better or worse?

• Obviously, ridgidity is of paramount importance.
• The wood will be well finished and sealed so I'm not really worried about expansion/contraction.

Thanks.

[RTP_Burnsville]

Hi,

Baltic Birch plywood is nice to work with. If you want to stick with solid hardwood I would use Hard Maple. It has fairly straight grain, is dense, and works well with sharp tools. In my area Ash, and Red Oak are available for about half the price as Hard Maple and would likely work just as well.

[martinw]

.....Im building it from hardwood. Without getting too distracted by the benefits or otherwise of hardwood, can someone please tell me the best hardwood to use for a cnc wood router considering the forces involved?
[/LIST]Thanks.

Hello,

Beech is good stuff to work with and has a nice straight grain. I've made a massive workbench using it. A really cheap source of the stuff is laminated beech kitchen worktops from IKEA. The worktops are 28mm thick, but you can laminate them with epoxy to go thicker.

Best wishes

Martin

[Geof]

Plywood is most likely the best choice because the strength is more or less the same along the length or the width; particularly the Baltic Birch which has a lot of thin plys. In addition plywood does not swell or shrink with changes in humidity as solid wood does.

Of course if you want to get really ambitious you can use Maple or Oak and laminate all your structural members together from thin strips. Somewhat like fancy boat building.

[thkoutsidthebox]

I was thinking about American Hard Maple or Oak. But I wasn't going to laminate it much at all. Was thinking that I'd just buy 2inch rough and cut my pieces as necessary. I have few parts in my design over 2" in thickness.

Thats a greak idea for cheap beech by the way, but Im not sure if it'd be the most suitable wood. Isn't beech slightly softer than maple or oak?

I was hoping to stay away from manufactured boards if I could. If I have the wood finished as if it was in an outdoors application will the expansion/shrinkage be fairly negligable?

[CNCkitsandBITS]

If I have the wood finished as if it was in an outdoors application will the expansion/shrinkage be fairly negligable?

First choice would be Birch ply and my last choice for a timber product machine frame would be any good quality ply.

But if you insist on using solid timber then using timber seasoned to around 19% (for out door use) would be a definite nono. Furniture quality timber is seasoned to around 8% and would be a much better choice. If you want the ideal buy the timber and leave it in your workshop for about a year (for hard wood) before you use it.

Best of luck,

John

[martinw]

I was thinking about American Hard Maple or Oak. But I wasn't going to laminate it much at all. Was thinking that I'd just buy 2inch rough and cut my pieces as necessary. I have few parts in my design over 2" in thickness.

Thats a greak idea for cheap beech by the way, but Im not sure if it'd be the most suitable wood. Isn't beech slightly softer than maple or oak?

I was hoping to stay away from manufactured boards if I could. If I have the wood finished as if it was in an outdoors application will the expansion/shrinkage be fairly negligable?

Dear TOTB,

IMVHO, there are several things you may need to consider in your choice of timber or sheet material.

Cost/ availability
Ease of working
Dimensional stability with change of moisture content
Ease of gluing
Strength

.. and others

OK, let's consider strength. IMHO, (1) hardness is not that important, nor is (2) shear strength, and probably (3) compressive strength or (4) the ultimate bending stress that can be resisted given the forces that are likely to be applied in this type of machine. What is really important is the ability of the material to resist deflection under load. Without wishing to get get too technical, (I probably have already, but that is one of my many weaknesses) this can be quantified by a property of a material called its "Young's Modulus". Fortunately, help is at hand with The Sagulator which calculates the deflection of shelves for a variety of timbers/sheet materials under different loading conditions. Here is the link...

http://www.woodbin.com/calcs/sagulator.htm

Crazy name!

Anyway, you can play around with different stuff and see how each deflects.

As regards the other non-strength characteristics, I have a hunch that moisture movement might never be entirely eliminated no matter what finish is used. That is just a guess. Others may help you on that issue.

Geof suggested a good quality close-grained plywood. IMHO, sound advice because, as he said, it has strength both along and across the face grain. By the way, if you go that route, pick a ply with as many veneers as possible. The only downside that I can see with his suggestion is the cost of dimensionally accurate (as regards thickness) ply sheets of this quality in Europe. North America will not believe the cost of stuff over here.

Sound familiar?

Best wishes

Martin

[ger21]

Geof beat me to what I was going to say. Laminations. But I'll get back to that.

If you look at the deflection calculator Martin posted, you'll notice that there isn't a lot of difference between species. Since there isn't a lot of difference there, I'd recommend using the most stable wood you can find. All wood moves, and when it's part of a larger structure, the entire structure will move.

Not sure how good this is, but I found a movement calculator you can download.
http://justwoodworking.com/software/wood_move.php

When working with hardwoods, budget will also come into play. The price of lumber is going through the roof, and it's going to keep going up.

One way to work around the movement issue, is to use glued up laminations. The downside is the extra work and time involved. And to make things easier, you'll want to have a jointer and planer. (And not that little handheld planer you have. ) Laminated beams are used in place of solid lumber in construction due to the increased strength. This is also desirable in a machine. You want it as strong and stiff as possible, and laminating is a good way to achieve that with wood.

For my router base, I didn't want to use standard construction lumber, due to the warping and twisting as it dries. The easy fix was to make laminations from it. I re sawed standard 2x4's ($2 each, so cheaper than hardwoods) into roughly 3/8" x 3-1/2" pieces, planed them flat, and glued them up into 12 layer laminations. Once dry, jointed and planed square, I had roughly 3" x 4" boards, that were very strong and stable, and have remained straight for a few years now.

If you want to (or need to) use any plywood, I'd only use Baltic Birch. Nothing else is anywhere near the quality, for the price. At least available around here.

Here's a pic of a leftover piece of the lamination I was talking about.

[Geof]

.....The only downside that I can see with his suggestion is the cost of dimensionally accurate (as regards thickness) ply sheets of this quality in Europe. North America will not believe the cost of stuff over here.

Sound familiar?

Best wishes

Martin

Oh I know the cost through visiting over there many times and doing business with a distributor of my products.

Mr Box Outsider Thinking; In My Humble Opinion, which is not humble at all, I think your least expensive and most effective approach will be to laminate.

And I just scrolled down the page while typing this and found that between me clicking on the Quote button and this page showing up ger came on the scene beating my game.

But he didn't mention that laminating also enhances stability through changes in humidity.

All in all laminating is by far the best choice.

[martinw]

Dear Gentleman,

This is indeed a very civil thread.

Best Wishes

Martin

[ger21]

But he didn't mention that laminating also enhances stability through changes in humidity.

I didn't actually say the word "humidity", but I did say

One way to work around the movement issue, is to use glued up laminations.

Since changes in humidity are what cause movement, it was implied.

[Geof]

I didn't actually say the word "humidity", but I did say



Since changes in humidity are what cause movement, it was implied.

Okay . But you never know with the Irish maybe it is necessary to be explicit .