Holes and MDF

[Upnxwood16]

So I have been looking at CNC Router designs for a couple of weeks now and I have seen too many builds to count. I came across this design in Google Sketchup for a 2'x3' wood router. I have not seen how they connected the two MDF boards together before in other builds and wondering if anyone has tried it in the past? I may just go ahead with it and see how it works.



The hole is 1" wide and 1" away from the edge on 3/4 MDF board. The bolt is 2 1/2" long and 1/2" width. I have attached a picture of it.

Thank you

[PaulRowntree]

It looks like they are trying to seat a flat nut against the inside of a curved hole; does not sound too secure to me, since strength would require doing damage to the MDF. If your drilling skills are sharp, you can use cross-dowels into a tightly fitting hole : the nut is a small barrel with the hole/threads at 90 degrees to the barrel body. You have to do pretty good alignment, but there is no play in them when done right. I buy mine at LeeValley (Canada). Plus, the holes are ~10 mm across instead of 25, so it weakens the MDF much less.

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Or, make the nut fit into a slot so the nut can sit against a washer, then press against a flat MDF surface.

I think that Patrick's machines use cross-dowels, and he has a host of videos on their construction.
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Cheers!

[Upnxwood16]

Thanks for the quick reply. That is what I was figuring also, looks like it would make disassembling and reassembling a snap. I will probably go the cross dowel route.

[Mountaincraft]

That's the method they are suggesting in the solsylva designs.. They're trying to keep it brain dead simple...

What I would suggest is to make yourself a template out of 1/2" MDF with a 'D' shape or a Rectangle shape, and then use your router with a bushing set to cut the holes... You'll have a nice flat surface to bolt against, and all your holes will have a clean finished consistent look to them..

[ger21]

Originally Posted by Upnxwood16 That is what I was figuring also, looks like it would make disassembling and reassembling a snap.

Personally, I'd recommend gluing the parts together and using the dowel nuts and bolts as permanent clamps. Gluing will add a lot of rigidity.

You can get dowel nuts at McMaster Carr. Just be sure to use a 10mm drill bit.

[jkarisny]

You could get a 1" diameter HDPE rod, slice it into pieces that match the thickness of the MDF and tap a hole in that. It will hold the threads better than MDF, and better than the nut shown in the diagram. Just a thought.

[Upnxwood16]

Wow a lot of different ideas an certainly some ideas to toss around.

[floodx]

From my research (not experience), this is what I would go with:

1) Tap the MDF itself
2) Put super glue in the tapped hole
3) Tap the hole again after

The super glue seeps into the MDF and expands. After it dries and you tap it again it apparently creates very strong threads that you can screw a bolt into without worrying about it coming loose. Can anyone else recommend this?

[Michael In Cali]

Originally Posted by floodx From my research (not experience), this is what I would go with: 1) Tap the MDF itself 2) Put super glue in the tapped hole 3) Tap the hole again after The super glue seeps into the MDF and expands. After it dries and you tap it again it apparently creates very strong threads that you can screw a bolt into without worrying about it coming loose. Can anyone else recommend this?

If I were not doing cross dowels, I would use Confirmat screws. They are the right screws for this material. No super glue required.

But, most likely, I would create rabbbets or dados and glue everything together without any fasteners. Continuous adhesion trumps point clamping for anything that does not need disassembly.

[Connor9220]

I built mine using 1/4"-20 bolts with cross dowels. It's really the right way to go. I didn't glue, as I wanted to be able to take it apart and adjust stuff, and make replacement parts as needed. I recently built a sound box for my vacuum out of 3/4" MDF. I used the Confirmat screws and they worked rather well. However, They're still not as nice as cross dowels for taking the machine apart and putting it back together because they thread into the MDF. After a few times taking things apart, they can get weak, and rip out, just like any other type of screw. If you do use cross dowels, do yourself a favor and make or purchase a drill guide, it'll keep you from going insane. Also, if you want, you can counter sink with a 5/8" forstner bit if you need to stack or have a smooth surface without the bolt head protruding.

[zhanx]

Originally Posted by floodx From my research (not experience), this is what I would go with: 1) Tap the MDF itself 2) Put super glue in the tapped hole 3) Tap the hole again after The super glue seeps into the MDF and expands. After it dries and you tap it again it apparently creates very strong threads that you can screw a bolt into without worrying about it coming loose. Can anyone else recommend this?

I can, I have done it before. For my table I am doing I am going to try Polycrylic from minwax and see how that holds up. Hoping it seeps in a bit more and holds stronger.

update just put the first coat on.

[CarveOne]

Flood the hole with the low viscosity (thin) variety of CA and it will seep in like water before before it kicks off. Don't use accelerator. It will get hot enough to smoke when it hardens and the penetration is deeper.

CarveOne