[dinkyguitar]

Hi All,

Part of my cnc router frame will be made out of MDF, but I'm not sure what type of screws to use...

Also, any suggestions on coatings, and using MDF will be appreciated..

dinky,

[DonFrambach]

When I make projects out of MDF, I try to avoid using screw threads in the MDF because I don't trust the MDF to hold threads very well.

I try to use bolts as much as possible to fasten MDF to MDF
I try to use wood screws to fasten the MDF to wood (not the other way around).
If I had to join an edge of MDF to an MDF face, I'd use cross dowels. Here's a link: Woodworking Assembly Hardware - Cross Dowels

Don't have suggestions for finishing MDF but there have been some real nice project here on CNCzone.com.

[osphoto]

Thanks for posting about cross dowels. Never seen that idea used. Thanks!

[Lee DeRaud]

When I make projects out of MDF, I try to avoid using screw threads in the MDF because I don't trust the MDF to hold threads very well.

I try to use bolts as much as possible to fasten MDF to MDF
I try to use wood screws to fasten the MDF to wood (not the other way around).
If I had to join an edge of MDF to an MDF face, I'd use cross dowels. Here's a link: Woodworking Assembly Hardware - Cross Dowels

Don't have suggestions for finishing MDF but there have been some real nice project here on CNCzone.com.

What he said, with a few qualifications:
1. Bolts are the right answer whenever possible. MDF (and solid wood and plywood as well) are strongest in compression - a fastener that squeezes the joint is much stronger than one that is pulling on it, i.e. screws.
2. If you don't need to take the joint apart after the fact, add glue to the mix. That's "in addition to", not "instead of", the bolts.
3. Cross-dowels are a gift from God. They allow a bolted joint to squeeze the MDF lengthwise. (See #1)

MDF is ridiculously easy to finish, at least compared to most woods...about the only thing you can't do to it is powdercoat. One thing that does improve the process is to flood the edges with very-low-viscosity cyanoacrylate glue. And I do mean "flood": do it until it drips. It wicks in and makes the edges nice and hard like the faces.

[ger21]

MDF is ridiculously easy to finish, at least compared to most woods...about the only thing you can't do to it is powdercoat

You can definitely powder coat MDF. We make TV cabinets for hospital rooms that are powder coated MDF.
It's a slightly different process than powder coating metal, so you need to find someone who specializes in it.


As for the best screws for MDF, look for Confirmat screws.

[Lee DeRaud]

You can definitely powder coat MDF. We make TV cabinets for hospital rooms that are powder coated MDF.
It's a slightly different process than powder coating metal, so you need to find someone who specializes in it.

How do you get enough static charge on it to get the powder to stick? (Or is that the "slightly different" part...)

[ger21]

How do you get enough static charge on it to get the powder to stick? (Or is that the "slightly different" part...)

Read this:
Powder Coating of MDF Application Process

[Lee DeRaud]

Read this:
Powder Coating of MDF Application Process

Huh. Wouldn't have expected the conductivity to be temperature-sensitive, but hey, if it works...

[dinkyguitar]

Thanks guys for all your info.

dinky,

[brtech]

Ditto on the cross dowels.

Confirmat is the right screw, but be aware they use a special, expensive drill bit. A good source is Woodworkers Hardware:
Search results for: 'confirmat'

[dinkyguitar]

Your not kidding about the expensive drill bit $48

dinky

[zool]

Structurally speaking, from a planning perspective and a construction perspective, the choice of fastening methods needs to address the statics and the dynamics of the design and construction, relative to the anticipated primary use of the structure.

Cabinets made from MDF generally only have to deal with static loading, and, on occasion, short-term trivial dynamic loading, therefore a confirmat screw is sufficient.

A CNC router made from MDF, as it is primarily used for controlling motion, should be thought of from a dynamical perspective, therefore the planning perspective and construction perspective should address the dynamic nature of the machine; specifically: the efficiently transfer and distribution of forces [ideally non-destructively] through the structural elements of the machine.

To control the dynamic forces of a CNC machine made from MDF, cross dowels are better than confimat screws, however threaded rod running the length of each structural element is even better. This method of fastening is a complete mechanical joining method that relies on only the threaded rod, washers and nuts [preferably self-locking].

To equally load the inside and outside of the structural members, make two pieces of each structural member, then route a grove for the treaded rod in BOTH pieces. Make the grove in each piece just over one-half the diameter of the threaded rod in both pieces. Glue and screw the MDF together.

On each corner, install an upper and a lower corner brace.

The result..BOMB PROOF.

And yes, I am a firm believer in overbuilding.


Watch this video about building a workbench on the Fine Woodworking site.

Getting Started in Woodworking: More Woodworking Basics for Beginners

On the slider on the right, go to the bottom, the video to watch is second up from the bottom.


The issues to be addressed in the design and construction of a CNC machine and of a woodworking workbench are exactly the same, that is, to use the forces and mass of the machine to cancel out the forces [which include vibration] of the machine. [Which is identical to the suspension/chassis design of an automobile.]


PS .. if you can find Sam Allen's book on building work benches, he has a similar design in that book. MAKING WORKBENCHES

[DonFrambach]

Structurally speaking, from a planning perspective and a construction perspective, the choice of fastening methods needs to address the statics and the dynamics of the design and construction, relative to the anticipated primary use of the structure.

Cabinets made from MDF generally only have to deal with static loading, and, on occasion, short-term trivial dynamic loading, therefore a confirmat screw is sufficient.

A CNC router made from MDF, as it is primarily used for controlling motion, should be thought of from a dynamical perspective, therefore the planning perspective and construction perspective should address the dynamic nature of the machine; specifically: the efficiently transfer and distribution of forces [ideally non-destructively] through the structural elements of the machine.

To control the dynamic forces of a CNC machine made from MDF, cross dowels are better than confimat screws, however threaded rod running the length of each structural element is even better. This method of fastening is a complete mechanical joining method that relies on only the threaded rod, washers and nuts [preferably self-locking].

To equally load the inside and outside of the structural members, make two pieces of each structural member, then route a grove for the treaded rod in BOTH pieces. Make the grove in each piece just over one-half the diameter of the threaded rod in both pieces. Glue and screw the MDF together.

On each corner, install an upper and a lower corner brace.

The result..BOMB PROOF.

And yes, I am a firm believer in overbuilding.


Watch this video about building a workbench on the Fine Woodworking site.

Getting Started in Woodworking: More Woodworking Basics for Beginners

On the slider on the right, go to the bottom, the video to watch is second up from the bottom.


The issues to be addressed in the design and construction of a CNC machine and of a woodworking workbench are exactly the same, that is, to use the forces and mass of the machine to cancel out the forces [which include vibration] of the machine. [Which is identical to the suspension/chassis design of an automobile.]


PS .. if you can find Sam Allen's book on building work benches, he has a similar design in that book. MAKING WORKBENCHES

In my opinion that was very well said!!!!!!!!!!!!!!!!!!!!