Building a Prusa i3 frame from 12mm MDF - Need help

Hi,

I would like to build a wooden frame using 12mm MDF which is the only I can find.

A friend can make straight cuts and I was thinking about making a simple box frame with 100mm (or more) wide strips.

My question is how to assemble the MDF strips to form a sturdy frame?

People normally use plywood, and use glue plus screws.

But 12mm MDF is not thick / strong enough to use wood screws without cracking.

What are the alternatives ways to assemble the frame?

Thanks in advance for your help.

J3d

Pre-drill.

I do a fair amount of woodworking, and use MDF for a lot of stuff. If you pre-drill the MDF so that it doesn't split, then you can make excellent joints using screws and glue. If your cuts are very good and straight, glue and clamping will also produce good to excellent results. Reinforcing certain areas by doubling the MDF can help with strength as well. Best results if you glue and clamp 2 payers of MDF together, and cut the joint edge afterwards.

Experiment with some scrap for what size hole you need to drill to get good grip with the screw threads, but no splitting. As a general rule though the screw threads don't need as much as you may think. It should be the glue doing most of the holding when the project is assembled, the screw mostly works to clamp the pieces together.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

I tried to pre-drill and for 16mm MDF (and thicker) it works well, but for this 12mm unless I drill a very large hole (in which case the screw does not do much) it cracks

I also tried doubling the layers but then the screw fall just in between the 2 sheets and only holds thanks to the glue also

countersink ? or longer screws.
machine screws and blind nuts.
metal corner brackets.
a piece of 1/2"(12mm) hardwood to use in the corners.
Cut interlaced slots. (you prolly already cut them flat I guess)

google this, "bracing a corner joint", to see lots of pics.

What do you have that you can use?

I will try with epoxy instead of wood glue and pieces of hardwood in the corners

On a current project, I'm using machine screws and tapping MDF. After drilling the holes, I flood them with CA glue, then tap them (after the glue dries).

I understand that this is the usual way of doing it, but the MDF I have is probably of a lower quality/density and cracks open very easily

Hopefully the epoxy will work...

The screws shouldn't actually do much when it's done. The glue should do most of the holding. If the quality of the material is poor, then you need to reinforce anyway, or you'll end up with a very poor frame. The role of the screws is mostly to clamp the joint tightly so that the glue can do its best work, and then provide a little bit of shear strength to the finished joint.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Thank you all for your help

I have now assembled the 12mm MDF frame with epoxy & pre-drilled/glued wood screws

That seems sturdy enough, so far so good

I have ordered stepper motors, drivers and the other electronic components

And while waiting for my delivery I am salvaging old printers/scanners for 8mm rods...

Old printers can also be an excellent source of stepper motors. Particularly old laser printers, but I think that some ink jets still use steppers for paper feed.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

I have not had any success finding stepper motors, only cheap DC motors, even the large laser printers I dismantled had brushless motors, this is why I ordered them

As for the rods, it seems that only HP uses 8mm stainless steel ones in their scanners, other manufacturers use anything from 6mm to 13mm or so

In case I cannot find all the rods required, I was considering buying 8mm OD (and either 6mm or 4mm ID) carbon fiber twill tubes to use with bushings: any advice about that?

steppersonline.com they have some of the best pricing for nema17, tho I wish their 34mm units came with connectors AND 1m wire.
PLUS they have shipping warehouses worldwide. No matter where I look, even bulk on alibaba it is very very hard to get below $10per stepper motor.

CF will work, see youtuber Tech2C corexy build for a discussion on using CF tubes as guide rails.

If HP uses 8mm rods, can you remember who uses 6mm ones?
In the USA I get 8mm and 6mm rods from Folgertech.com, a great supplier.

Your link does not work ("SteppersOnline.com is for sale")

The 6mm rods I found in a Canon and in a Dell branded printer (made by Lexmark): that was a disappointment because what served as guide for their scanner was a mere fold in the plastic frame.

I saw what Tech2C did, and this encouraged me with CF, but he used 10mm diameter tubes which may be a bit much for what I am making.

The price for 8x4 or 8x6 CF tubes is much less than SS, they should be stiff enough and if the tolerance on the OD is acceptable (which I do not know) that would be a great option

apologies, forgot the omc-,

[www.omc-stepperonline.com]

For the CF rods I found 5x7mm tubes, rolled construction (I understand that the pulltruded are not suited because only strong longitudinally, not across their main axis) for under $2 per 500mm length, how does that sound?