[iamadude]

Hi everyone,

I am planning to build a CNC router, MDF build, at the size of 4' by 2'. The router is aimed to cut wood for the most part, but would be nice if it was able to do some light aluminum. I'm still designing, so I was wondering what would be a good thickness of the MDF to use as building material? I have some 1/2" MDF left from my previous project and I thought I could use this for some parts of the router (e.g. z-axis/spindle carriage). But what should be the gantry side thickness? If I laminate 2 layers of 1/2" MDF for 1" thickness, would that be a safe bet?

Thanks!

[ger21]

I would laminate at least 3 layers for the sides.
For anything else, I would not use 1/2" at all. Ideally, you'd want to make all the components using torsion box construction. Single layers of MDF will warp and sage, and are not rigid enough to build a decent machine.

[iamadude]

Thanks for the quick reply Gerry. I'll make the modification for 3 layers.

About using single layers of MDF, wouldn't sealing and then painting over the surface protect against warping? I was thinking about using 1/2" sealed&painted MDF because I saw some builds that used the this approach and it seemed to work fine.

Also, I've looked over some threads about building a torsion box. I'm not sure if I have the skills or equipment to make a flat and decent torsion box. I'm planning to order laser cut for my MDF parts. Then after this CNC router is done, perhaps use it to cut out the ribs that I can use for a torsion box upgrade.

Thanks,

Bill

[iamadude]

Thought I might as well attach my design so far, and maybe someone give me some advice and point out what I should fix.

Here it is:

Thanks!

[CNCSammy]

Here the book I used to build my CNC machine:

Build-Your-Own-CNC-Machine

This machine is all in MDF and is working great for my needs. Basically, the main table (X axis) is two 3/4" MDF sandwiched together. Almost everything else is 3/4" MDF to the exception of the gantry rail (Y axis) that is also two 3/4" MDF stacked together.

[wizard]

If your are serious about aluminum machining I'd avoid MDF. if you limit the machine to wood then MDF certainly can do a credible job. Even so I'd be reluctant to use MDF. That is a personal bias but I really don't like the stuff. You might want to look into some alternative "wood" builds here. Everything from plywood to bamboo planks have been used to build CNC machines.

Thanks for the quick reply Gerry. I'll make the modification for 3 layers.

About using single layers of MDF, wouldn't sealing and then painting over the surface protect against warping? I was thinking about using 1/2" sealed&painted MDF because I saw some builds that used the this approach and it seemed to work fine.

With mainstream MDF you absolutely need to protect it from moisture.

Also, I've looked over some threads about building a torsion box. I'm not sure if I have the skills or equipment to make a flat and decent torsion box.

Flat surfaces are key to making a machine that runs well, you will need to select a construction method that leads to flat and square surfaces. Generally that is easier if you have the correct wood working machines.

I'm planning to order laser cut for my MDF parts. Then after this CNC router is done, perhaps use it to cut out the ribs that I can use for a torsion box upgrade.

Thanks,

Bill

That sounds like a lot of screwing around honestly. Further you are going to need longer travels than what your CNC has. You can have the sheet goods cut at a decent supplier for ribs for your torsion box. I'm thinking parallel cuts here with you having to finish up cutting any details. If you are really worried about your abilities I'd suggest purchasing a gantry beam of Steel or aluminum. A well done gantry is key to building a great machine. Given that it might not be a bad idea to bone up on the skills required to do these long flat surfaces. The fact is a metal gantry beam will likely be more expensive.

I say likely because it isn't a given.

[wizard]

Q

Thought I might as well attach my design so far, and maybe someone give me some advice and point out what I should fix.

Here it is:

Seems complicated. Plus im not sure why you are using only one linear rail for the Y axis.

Thanks!

As was mentioned already inn another post, if you are going to use MDF you need to laminate it up to make a decent beam. I realize that you are only shooting for only 2' of working space for the Y axis but you will still want a stiff beam. At a minimal I'd shoot for 3" of thickness for a six inch high beam. Frankly that may be a bit on the thin side. However by laminating pieces of flat stock together you eliminate the need to fabricate a torsion box beam. I'd mount your round rails on the face of the beam.

Remember keeping it simple means less difficulty in getting it done. Also the numbers thrown out above are wild, the beam needs to be sized to properly support your Z axis based on the amount of Z clearance you have.
Like wise the Z needs to be a simple yet surf design

Beyond all of that your X axis needs more support. In the picture it looks like the linear rail is bigger in diameter then the beam it sits on is square. These linear components need stiff flat surfaces to support them, they do not support themselves. You don't need to go the extent of the Y axis gantry beam as it is completely possible to brace the X axis support.

[iamadude]

Hi wizard, thanks for all the advice!

I should say that this machine will likely be only used for cutting wood material; I meant to say that aluminum machining would a nice feature, but I don't think I'll use the machine for that purpose.
So let's just say this machine is only for cutting wood material.

I decided to use MDF here because I saw threads commenting that it's a more stable, cheaper and a flat material that can be easily worked.

Q
Seems complicated. Plus im not sure why you are using only one linear rail for the Y axis.

I only put in one linear rail for the Y axis because I thought these rails are suppose to be strong; and I didn't mention this before, but the machine will be cutting wood, so I thought one linear rail and one round rail would work fine here.

Q
As was mentioned already inn another post, if you are going to use MDF you need to laminate it up to make a decent beam. I realize that you are only shooting for only 2' of working space for the Y axis but you will still want a stiff beam. At a minimal I'd shoot for 3" of thickness for a six inch high beam. Frankly that may be a bit on the thin side. However by laminating pieces of flat stock together you eliminate the need to fabricate a torsion box beam. I'd mount your round rails on the face of the beam.

Since now that I intend to cut only wood on this machine, should the gantry sides still be laminated to 3" thickness? That seems a lot to me.

Q
Beyond all of that your X axis needs more support. In the picture it looks like the linear rail is bigger in diameter then the beam it sits on is square.

Sorry about the bad picture, the linear rail section is kind of unclear in that. But the linear rail is smaller than the steel beam it's sitting on.

Thanks,

Bill

[whimsical]

The bearing spacing on the long axis looks way to close to me
The bottom rail on the short axis takes the highest load so make that the best slide. Not sure which of your round fat rail or the supported rail is the stiffest.
Read through this long thread and take particular notice of the posts by dmalicky, he has great knowledge.
http://www.cnczone.com/forums/diy-cn...cad-posts.html

[iamadude]

The bearing spacing on the long axis looks way to close to me
The bottom rail on the short axis takes the highest load so make that the best slide. Not sure which of your round fat rail or the supported rail is the stiffest.
Read through this long thread and take particular notice of the posts by dmalicky, he has great knowledge.
http://www.cnczone.com/forums/diy-cn...cad-posts.html

Thanks for the advice, I'll make sure to check out the thread.

[wizard]

Hi wizard, thanks for all the advice!

I should say that this machine will likely be only used for cutting wood material; I meant to say that aluminum machining would a nice feature, but I don't think I'll use the machine for that purpose.
So let's just say this machine is only for cutting wood material.

If the vast majority of your work is wood then I'm not as concerned about a machine built out of wood. The problem with maching metals is the temptation to use lubricants or coolants which can raise hell with wood especially MDF. You can of course machine some materials dry but you compromise by doing so.

I decided to use MDF here because I saw threads commenting that it's a more stable, cheaper and a flat material that can be easily worked.

It is cheap and easy to work with, as for stable it gets real nasty if wet. Personal perspective:
The bad:

1. MDF is really nasty to work with, the dust is down right terrible.
2. the material isnt stable when wet, in fact it decomposes.
3. It doesn't hold conventional fasteners well.
4. Damages easily

The good:

1. the sheets are flat
2. the material deadens vibration.

I only put in one linear rail for the Y axis because I thought these rails are suppose to be strong; and I didn't mention this before, but the machine will be cutting wood, so I thought one linear rail and one round rail would work fine here.

I just thought it to be strange. Being a build out of wood I'm not sure profile rails are worth the expense. Further round rails provide slightly more capability to handle seasonal movement in wood.

Since now that I intend to cut only wood on this machine, should the gantry sides still be laminated to 3" thickness? That seems a lot to me.

It really isn't a lot, it is slightly less than a common 2x4 is high or slightly more than it is thick. Even with your short span I'd look at 3" as minimal for a gantry this size made out of MDF. It isn't like it takes a lot of material either. I mention this in the context of a laminated beam, if you build a torsion box beam I'd go even bigger to better leverage your available materials.

The thing to remember is that the forces being applied will tend to twist that beam. The better the gantry resist twist the better your precision and surface quality. I guess I look at it this way, if you are about to buy a sheet of MDF you might as well put it to use in a positive way.

Sorry about the bad picture, the linear rail section is kind of unclear in that. But the linear rail is smaller than the steel beam it's sitting on.

Thanks,

Bill

For the X axis frame I'd suggest components of at least 2" square. With bracing from the table support that generally works out well on smallish low cost machines. Your picture was misleading in this respect. In an ideal world you would use larger components to put more mass into the base of the machine. Heavy helps with vibration and can aid in keeping the machine from walking around.

[iamadude]

Thanks for the detailed replies wizard!

You make lots of good points. I'll redesign my machine with that in mind.

Thanks!

Bill