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Frames...accuracy and/or upgrade???

Posted by andrew76092 
Frames...accuracy and/or upgrade???
April 14, 2016 02:47PM
Greetings,

I’m in the beginning stage of building a Mendel90 but am have a few questions I’m hoping someone will be able to answer. Many thanks in advance:

1. Ideally, I was going to build the “sturdy” version of the Mendel90, using the 12mm MDF. However, in the USA, sourcing 12mm MDF is virtually impossible as everything is cut in inches and not millimeters. That said, the closest cut of MDF to 12mm is not exact. How critical is the 12mm? Should I scale up or down to the 12mm?

2. I’ve learned that vendors are selling upgraded frames, bypassing acrylic and MDF and going with aluminum. I’ve found the basic kits for around $150 but want to be sure they are compatible with my electronics, motors, 3D printed parts, et al. These frames mention Prusa and i3 upgrades and nothing about Mendel90. What would be considered the “upgraded” frame for the Mendel90 if I chose to go that route? Being that I have all the 3D printed parts, electronics and virtually everything needed to build (except the frame), I’d consider this upgrade but want to get the right one.

Again, many thanks in advance!

Andrew
Re: Frames...accuracy and/or upgrade???
April 15, 2016 12:24AM
The only place the exact thickness matters is where the spool holders hang over the frame. If you are printing the parts yourself you could generate them slightly bigger or you could file the plastic or chisel the wood a to make them fit. A lot of people use different spool holders anyway.

The best material for making a Mendel90 is Dibond aluminium composite but you need a CNC to make that version. The Prusa I3 is a different machine entirely.


[www.hydraraptor.blogspot.com]
Re: Frames...accuracy and/or upgrade???
April 20, 2016 12:39PM
Quote
nophead
but you need a CNC to make that version.

Is this an overstatement?

I am planning to build my frame with 3mm comp. intent is to cut the panels by Dremel with the bit below... thought my biggest problem would be with plastic fouling the bit- is there something I'm overlooking?


Re: Frames...accuracy and/or upgrade???
April 20, 2016 01:57PM
Because the dibond version was designed to be cut with a CNC I took advantage of that and made some of the holes slots and rounded the corners. The sturdy MDF design was designed to be made with hand tools so has only round holes and square corners.

For cutting Dibond with a router you want a single spiral fluted endmill like these: [www.frezycnc.eu]. I don't know if a Dremel is up the the job. I use an 800W Kress spindle motor.


[www.hydraraptor.blogspot.com]
Re: Frames...accuracy and/or upgrade???
April 21, 2016 09:57AM
I built mine with 3mm Dibond with my simple home tools and all went and is still fine.
Only thing is the sheets should be cut square by a circular saw or something where you have the sheets really square.
I ordered mine here: [www.electronic-things.de]
Hopefully you can find a shop where you can order them cut to size. The rest can be done by hand without special tools.
Re: Frames...accuracy and/or upgrade???
April 21, 2016 10:49AM
Quote
nophead
...designed to be cut with a CNC I took advantage of that and made some of the holes slots and rounded the corners.

For cutting Dibond with a router you want a single spiral fluted endmill... ...I don't know if a Dremel is up the the job. I use an 800W Kress spindle motor.

Ahh, okay- kinda what I was thinking. When I compiled the plans for my machine I set the cnc_flag to false and as I just thumbed through my drill sheets it looks as though the rounded corners are still there but all the drill holes are all holes, not slots.

Wow. Those are some pretty wicked looking bits. Underpowered Dremel- but for a one-off job? Perhaps one of these would be better suited?


Quote
danielis
I built mine with 3mm Dibond with my simple home tools and all went and is still fine.
Only thing is the sheets should be cut square by a circular saw or something where you have the sheets really square.
I ordered mine here: [www.electronic-things.de]
Hopefully you can find a shop where you can order them cut to size. The rest can be done by hand without special tools.

I made half-an-attempt at getting the frame sourced and cut locally but the places I found online didn't seem all that interested in such a one-off small job. I was able to find an ebay seller that shipped me a 2'x4' sheet for what seemed reasonable.
My original plan was to use a straight-edge and utility blades to get the panels squared but was stumped on the inside cuts on the gantry- before the Dremel it was a jig-saw and lots of concentration. Briefly considered getting a mini-saw attachment, but didn't immediately see any blades that seemed to be a good fit.

But yeah- as it stands... I'd still like to find a way to use the Dremel. If I can find an an appropriate bit I still think I can manage it with a drywall square, a cutting base attachment [www.dremel.com] and slow cut speed (high-ish spindle speed, slow me moving the tool... low manual feed rate, I guess?).
Re: Frames...accuracy and/or upgrade???
May 03, 2016 02:44AM
Hi,

You can work Aluminium Composite Panel (ACP, Dibond) by hand if you have the time and take care. As one of my old mentors would say "Cut wide and fettle!".

If you buy a large enough sheet you can take the critical edges (the ones that must be straight) from the outside edges of the material. On the Mendel90 this is achievable because only the rear struts require two straight edges so use the material corners for them.

Careful cutting using a jigsaw (with an appropriate blade) followed by lots of filing should produce an acceptable result. Of course, nophead's method of using a CNC router is preferred for bulk production like he used to do.

Regards,
Neil Darlow


I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.
Re: Frames...accuracy and/or upgrade???
May 03, 2016 06:12AM
I made my first Dibond mendel90 by buying sheets cut to size and with rounded corners from here: [www.cutplasticsheeting.co.uk]. Beware they often send sheets with scratches and / or slight warping and they substitute generic ACP for Dibond.

The only cutting I needed to do myself was the big hole in the gantry. I drilled the holes using the PDF templates, an optical centre-punch and a spot drill. At that time the design wasn't optimised for CNC, so it didn't have any slots or mouse holes, only round holes like the sturdy. There is a cnc_sheets option in the config that you can set to false to get back to that but it changes everything: plastic parts, sheet drawings and BOM.


[www.hydraraptor.blogspot.com]
Re: Frames...accuracy and/or upgrade???
October 08, 2016 10:29AM
Sorry for the belated reply... I built mine using 1/2 inch MDF. I just had to use a craft knife to cut the notches out wider in plastic components that actually hook over the edges of the MDF (like spool holders). If you print the parts in ABS, it's easier than if you use PLA (the ABS cuts easier). I used black polyurethane brushed onto the MDF bafore assembly to act as a moisture seal (4-5 coats, since the MDF, especially the edges, soaks up the poly like a sponge)

Edited 1 time(s). Last edit at 10/08/2016 10:43AM by Rich K..
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