[bevins]

Why is many people using MDF instead of plywood? I would think because of the inherent problems with moisture with MDF that plywood would be better to use than MDF. 9 ply 3/4, 5/8 or 1" plywood seems to me would be sufficiant and plenty strong enough.

Can someone shed some lite on this? I have been researching and lurking here trying to figure out which router table I want to build. I have the funds and ability to constuct in aluminum, minus a mill, but wonder if it is a good idea to start with an metal build.

I will use the machine to build electric guitars, engraving, tube amp parts, and need the ability to machine small aluminum/metal parts. I have purchased a few plans, and I am still wondering which way I should go. I have been really close to diving in with data-cuts metal table or joes mdf/plywood table.

Can someone sum up the pro's and cons to metal vs mdf/plywood?

Thanks in advance, and this is a great place.

Bob

[thkoutsidthebox]

AFIK:

Metal gives a more ridgid finished table.
Metal is more expensive.
Metal requires different tools to work that not everyone has available.

If you have the equipment, then working metal, or working wood, its all the same. A 3x6 inch square is the same square whatever its made of. But some people only have the equipment/budget/experience to build from wood. Im building from wood because I dont have the tools or budget right now to build from metal. Next table will be from metal. If you can go with metal, I would.

[ger21]

For most people, wood is cheaper and easier to work with than metal.

As for MDF vs plywood, MDF is much more stable. Unless you use good quality baltic birch ply, most plywood sold today will warp severely if not cut and assembled within a day or 2 of being puchased, provided you can find flat plywood to start with. If you seal and paint your MDF, you really shouldn't have any moisture problems.

[drmosh]

ok so a few points...

for the sake of these comments i'm going to assume you would use 11 or 13 ply birch plywood, not the cheaper grade stuff.

plywood and mdf are both going to react with their atmosphere - humidity to be exact. BOTH must be sealed to be stable. plywood will warp/bow and mdf will flare at the edges.

plywood is much much MUCH stronger (tensile and compressive) than mdf. there is a reason no boats are made of mdf (and it's not because mdf isn't waterproof). however, mdf is more rigid. there are some things that could also benefit from plywood providing better dampening and strength.

a popular sealing method for plywood is very low viscosity epoxies - a few coats of this stuff and your plywood is crazy strong. you can do the same on mdf but you have to be very careful not to overapply and saturate the material. mdf is much more porous than plywood. my opinion is that it's better to seal mdf with a barrier coat (like a paint or primer) than a penetrating sealer (like diluted epoxy).

mdf is an engineered material that is effectively flat on it's surfaces. plywood is not flat, even the very best stuff. also, mdf machines very nicely and uniformly.

plywood weighs approx. 25% less than an equivalant amount of mdf. heavier does not always mean better/stronger...

at the end of the day, plywood is a really amazing product that outperforms many other materials on a pound-for-pound basis. however you have to buy the good stuff and that gets expensive, and it's harder to find. also, you loose the close tolerances that you get with mdf. you could make a router completely with mdf, but it would be tough to make the same router with the same tolerances using plywood. HOWEVER - you could make a stronger and lighter router using a mix of both!

[Madclicker]

ok so a few points...
for the sake of these comments i'm going to assume you would use 11 or 13 ply birch plywood, not the cheaper grade stuff.

When you are talking about the suitibility of plywood for use as tooling it doesn't matter how many plys, or what the surface is finished in...birch, oak, maple makes no difference. What matters in the stability of the ply is whether the inner plys are consistant. Like Ger said, baltic birch is the best plywood you can buy. In my experience it move much more than MDF, but it's the best ply I can get.

[QUOTE=drmosh;239505]

plywood and mdf are both going to react with their atmosphere - humidity to be exact. BOTH must be sealed to be stable. plywood will warp/bow and mdf will flare at the edges.

I have no flaring of MDF and I live in as humid a place as there is. Plywood, on the other hand, is a royal pain. Again, like Ger said, you are lucky to get flat ply off the rack, and if you do you better use it quickly.

plywood is much much MUCH stronger (tensile and compressive) than mdf. there is a reason no boats are made of mdf (and it's not because mdf isn't waterproof). however, mdf is more rigid. there are some things that could also benefit from plywood providing better dampening and strength.

I'm not a materials engineer, but I think ply is whimpy compared to MDF. You'll never get me in a boat made of MDF!!!!!

a popular sealing method for plywood is very low viscosity epoxies - a few coats of this stuff and your plywood is crazy strong. you can do the same on mdf but you have to be very careful not to overapply and saturate the material. mdf is much more porous than plywood. my opinion is that it's better to seal mdf with a barrier coat (like a paint or primer) than a penetrating sealer (like diluted epoxy).

My choise of sealer for MDF is phenolic laminate.

mdf is an engineered material that is effectively flat on it's surfaces. plywood is not flat, even the very best stuff. also, mdf machines very nicely and uniformly.

I agree

plywood weighs approx. 25% less than an equivalant amount of mdf. heavier does not always mean better/stronger...

Sometimes it does.

at the end of the day, plywood is a really amazing product that outperforms many other materials on a pound-for-pound basis. however you have to buy the good stuff and that gets expensive, and it's harder to find. also, you loose the close tolerances that you get with mdf. you could make a router completely with mdf, but it would be tough to make the same router with the same tolerances using plywood. HOWEVER - you could make a stronger and lighter router using a mix of both!

I work with both every day...literally. MDF is flat and stable. Plywood sucks to work with, but it's the only way to make attractive wood cabinets. For tools, give me MDF everyday.

Be careful who you explain the shortcomings of plywood to! Some guys wanna start crying!

[dertsap]

You'll never get me in a boat made of MDF!!!!!

!

if the fish are biting i'd be out there in a minute ,just don t expect me to have the strength to pull that swelled up sponge back up onto shore

[cut more]

Madclicker,
Could you tell me what phenolic laminate is? I need to seal the mdf on my router and have been trying to find out what works.
Thnx

[ger21]

Madclicker,
Could you tell me what phenolic laminate is? I need to seal the mdf on my router and have been trying to find out what works.
Thnx

Formica

[CurtisU]

I agree with drmosh, if it's gotta be ply or mdf, a mix of the two would be best... if you can get the good stuff.

My Joe's ish project is all mdf, heavy as a heavy thing, and taking a very long time to build. I had a guitar project going at the same time.

If you need to get up and running fast you should consider buying a metal one off the shelf. If you must build and can, I'd push you toward metal, only because it's likely to be more robust. Better to be building guitars rather than repairing your tools.

If it's gotta be "wood" consider a kit, precisely cut parts for torsion box type construction are tough to do by hand.

If I'd have had a supply of baltic birch (BB) ply I would've used it in the majority of the gantry and Z for weight savings. My hope is to find a supply of BB ply and use my completed router to redo those parts. I prefer the look of ply and a coat or two varnish is all that's needed to seal it, my mdf gets a coat of primer and two of paint.

Curtis

[Madclicker]

Formica

Yep, that's a brand name. Beats the crap out of paint.

[bigz1]

Yep if you cant afford steel go for MDF for all the reasons outlined and if your concerned about moisture, buy moisture resistant MDF(usually identifiy by the green coloured core).

As for sealing MDF if its formica faced edging tape looks good otherwise use high build water based MDF primer(can be spayed or brushed dries quickly and is extremely easy to sand and fills the pores in 1 coat). Available to the UK from Screwfix in small quanties for approx £20.

[Coogrrr]

I would think that if you buy a sheet of 1/2 mdf sandwitch it between 2 1/2inch ply (almost anything) completely coat surfaces with glue lay on garage floor and set several buckets of rocks to hold them together. When dry cut board and put 1.75inc screws thru boards in both directions.

wouldnt you end up with a cheaper (thinner parts and cheaper products) yet stong as all hell solution compared to all the BB or laminating the hell out of mdf?

last stupid thought was after enough BB or mdf and lamination could you just buy some steel and pay to have it welded for cheaper?

I am going all steel and aluminum and am looking to build for .0001 tolerance based off of Solsylva.com plans large belt table.

insert shameless plug here...
http://www.cnczone.com/forums/showthread.php?t=29877
end shameless plug...

(nuts)

[ger21]

I would think that if you buy a sheet of 1/2 mdf sandwitch it between 2 1/2inch ply (almost anything) completely coat surfaces with glue lay on garage floor and set several buckets of rocks to hold them together. When dry cut board and put 1.75inc screws thru boards in both directions.

wouldnt you end up with a cheaper (thinner parts and cheaper products) yet stong as all hell solution compared to all the BB or laminating the hell out of mdf?

Buckets of rocks don't really provide enough clamping force to do that job properly. You need clamps, lots of them, or a vacuum press.

last stupid thought was after enough BB or mdf and lamination could you just buy some steel and pay to have it welded for cheaper?

Where's the fun in that??

[Coogrrr]

Buckets of rocks don't really provide enough clamping force to do that job properly. You need clamps, lots of them, or a vacuum press.



Where's the fun in that??

I dunno just thought maybe it would be kwik and cheeep. Anywho I am interested if there is a way to slap 2 or three sheets of something with glue and screw together that would make a non-warping piece, I ask as I may do something like this on a smaller second table.

[randyf1965]

Use your router to cut a torsion box for a new table...... the interlocking torsion frame work cut from 1/4" mdf (or plywood) with a 1/4" skin on both sides (wouldn't be a torsion box without.....) is very easy and extremely strong (glued and nailed)

[SZID]

Interesting points & advice!

I have come here trying to determine if Baltic Birch Ply can come close to aluminum's performance while saving some $. I have built many items/gigs/furniture/etc using both MDF/HDF and Baltic Birch. Baltic Birch is very good (often refered to as either Baltic, Russian Ply or European Plywood). It is made of birch which is a hardwood and because it is super laminated it already contains a good level of sealant in the adhesives binding its layers together...the low viscosity expoxy would be perfect as a finished coating. BB holds brad nails like a tiger, drills/routers very cleanly for holding t-nuts and is available in 5'x'5 sheets in 1/2" 3/4" 1" thicknesses. I have found the stock at Toronto's Century Fairbank Lumber to be superb, flat stacked and high quality.

BB was once used in building aircraft frames...laminated into 1.5" member it is dangerously strong. I am considering building a CNC router with this once I research a little more. I believe side frame rails in the 2X4 size can work very well with hardened 1/2" rod on the top and bottom to engage with V roller bearings.

My $.02-------hopefully worth gold.

-SZID

[mykrowyre]

Modern MDF is mostly GLUE. So it's far more stable than plywood which is layers of wood, glued together with gaps. As for birch, it is not what it used to be. To get good quality (aircraft or marine grade) birch, it's VERY expensive. Home Depot sells birch, and I've used it here and there, but it tends to delaminate and is not very good quality.

To me it was not worth the effort.

After weighing the options, I decided to go with 80/20. I couldn't bear the thought of coming out to my workshop in the hot summer to find my CNC warped from humidity.

I figured I'd spend the same amount of money rebuilding/repairing a wood cnc as I would have spent to build it right the first time with 80/20. Plus, the 80/20 can be ordered pre-cut to length.

[SZID]

Understood about 80/20. The thing is, we're looking to cut aluminum and 80/20 alone rings like a tuning fork unless it is properly dampened for vibration.

We are considering epoxy-foam filled 80/20 (plus other modifications) OR utilizing the natural characteristics of Baltic Plywood which would do this very well. NOT BirchPlywood from HomeDepot...we're talking BALTIC RUSSIAN PLYWOOD (highgrade) with significantly more thin veneers of birch, it is heavily impregnated with adhesive. These layers are very uniform..no voids.

Baltic Birch may very well have more resistance to temp than alum and humidity should not be a problem if edges and outer surfaces have coating of epoxy. Its heavier weight may also help to damped vibration/chatter. Many useful benefits... easier to work with and less cost than alum. Best way to varify is to try it which is exactly what we must do


-SZID

[mykrowyre]

Understood about 80/20. The thing is, we're looking to cut aluminum and 80/20 alone rings like a tuning fork unless it is properly dampened for vibration.

We are considering epoxy-foam filled 80/20 (plus other modifications) OR utilizing the natural characteristics of Baltic Plywood which would do this very well. NOT BirchPlywood from HomeDepot...we're talking BALTIC RUSSIAN PLYWOOD (highgrade) with significantly more thin veneers of birch, it is heavily impregnated with adhesive. These layers are very uniform..no voids.

Baltic Birch may very well have more resistance to temp than alum and humidity should not be a problem if edges and outer surfaces have coating of epoxy. Its heavier weight may also help to damped vibration/chatter. Many useful benefits... easier to work with and less cost than alum. Best way to varify is to try it which is exactly what we must do


-SZID

Ahh ok. Makes sense to me. I agree real high grade russian plywood is some fantastic stuff! I'm surprised it's not more expensive than 80/20. But I understand why you don't want to go with 80/20... it does ring like crazy!

[ger21]

I'm a big fan of building with wood. But you need to do it right. I'm currently working on a large wood machine. Baltic birch, torsion boxes as well as some custom laminations. The goal is to have a very high performing machine.
As you said, they used to build planes our of wood. They also build very big and fast boats from wood. It's all about how you use it.

Here's some pics of the parts for my spindle carriage. I haven't assembled it yet, but it should be incredibly strong. It's also very compact. About half the size of the one on my first router. It's baltic birch with Makore veneer.
http://www.cnczone.com/forums/691923-post172.html