How thick does an aluminum print bed need to be
I am extending the bed of my TronXY X3 FDM RepRap printer.
I am extending the bed from 220 mm x 220 mm to 220 mm x 300 mm. For now, I will keep the existing bed and add and aluminum sheet on top. That leaves 40mm on front and back of the original bed.
Right now I only plan on running PLA; but, I do plan on heating the bed.
How thick does the aluminum sheet need to be?
You are adding 380mm to the size of the bed, and that only leaves "90mm on front and back"? Is that a typo, and did you mean 190mm? It doesn't sound like a very good idea to just put a big slab of aluminium on top of your existing bed, because it won't be very rigid and will vibrate all over the place. I think you should change to a different carriage design if you want to do this.
@TomvanderZanden the real typo was that I said 600mm when I should have said 300mm. 600mm would have been a HUGE base - COOL but un-realistic for an X3 base. Regarding attaching the aluminum to the plate, I attach my glass plate now; but, then you were probably referring to my description of a plate that had more unsupported material than supported. With the right numbers, the overhang is small compared to the overall size.
@TomvanderZanden I found a random piece (23" x 6") of 1/8" sheet aluminum, paper-clipped it to the bed and started printing on it tonight. Funny that it is almost as long as my original 600mm typo. I figured what the heck, best way to see what I learn. Getting it leveled was a bit challenging (I don't have auto-level) - several failed prints (some of which were exasperated by not getting glue stick down everywhere). Print is 245mm long - so just a little longer than the original bed. New "bed" overhangs over 4" in front and back. Pretty comical - but it works. ;)
Main factors that control the process of the print bed selection are
- weight: too thick plate increases inertial force, limiting maximum acceleration/jerk (decreased print speed)
- stiffness: too thin plate will warp when heated or bend during calibration (decreased print quality/printer reliability)
For table sizes around 400x400mm I would think of 4mm plate, but it still can warp if heated unevenly.
Sometimes it makes sense to use a sandwich-type table: lower level is MDF, cork panel for heat insulation and thin (1.5-2mm) aluminum heated bed on top.
A sandwich table is great for higher bending strength at a lower mass. Heating it can be a challenge, as most of the interior materials are relative insulators. You could consider a layered structure with a PCB/heater on the top layer, something light but incompressible for the middle, and more PCB without the heater traces for the bottom. What to use for the middle? Ideally, something like an epoxy similar to PCB material foamed with air and hardened. Maybe an epoxy/pearlite mix. If you have a CNC router, you could make a gridwork of PCB strips on edge.
I build an 18.5" diameter delta printer. The bed was 3/8" thick 6061 aluminum. It is plenty stiff, but it takes an hour to heat to 100°C. When I rebuild it, I'll probably drop down to 1/4" and increase the heater from about 250 Watts to 750 Watts. That should heat the bed in 15 minutes, which is still a long time. Waiting for the bed to heat for ABS is one of the greatest frustrations with that machine.
For your machine, how much the 1/8" plate bends will depend a great deal on which aluminum alloy and temper you use. From OnlineMetals.com, 6061-T6 and 7075-T6 are available. 7075 is slightly stiffer, but both should be good enough. 6061 is half the price.
I highly recommend aluminium tooling plates. They have a +/- 0.1 mm flatness tolerance on 1 meter. It's alloy 5083 offers a great stability. You can purchase such for example at aluminyumburada, which offers custom cut piecees.. They have a minimum thickness of 5 mm, though the prices get lower the thicker the piece is.