Open source CNC Plasma cutter, a general idea and a lot of info.

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14 Mar 2019 16:25 #128595 by tommylight
Dust from plasma cutting is very fine and very sharp so it can do quite some damage to rails and bearings. Having a water table diminishes that problem a lot, but not totally, so daily cleaning of rails is a good practice.
Not seen any failed bearing on AC servo motors yet, same goes for DC motors and steppers.
Have seen what the dust from the brushes gathered at the motor commutator can do on DC brushed motors, from messing up the tuning during work to getting very hot with very little use and heating the drives to the point of shutting off.
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15 Mar 2019 20:17 #128683 by tommylight
I do need some opinions here,
I am thinking of doing a small machine with simple bearings, since i used that over 10 years ago i really did not like them for linear movement at all. What do you guys think?
Usually up to 2 meters in length ( 80 inches ) i use round rails, 30 or 35 mm diameter with corresponding linear bearings, the problem with them is that with no support they do sag a bit and i can not find bearing holders here so i have to improvise.
If used with a THC, the sagging problem is non existent as the THC takes care of that difference easily. Without a THC they are usable only up to 1 meter in length.
The main issue right now is i am out of stock on long linear rails, got some THK 45mm left and some short 35mm and 30mm.

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16 Mar 2019 08:49 #128719 by Grotius
Hi Tom,

I have made many machines with roller bearing's. They are all still working after 6-7 years.
It's a cost effective solution. The market for cheap machine's is bigger then for expensive machine's.
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16 Mar 2019 13:19 - 16 Mar 2019 13:20 #128734 by jmr
Hi,
Do you have any opinion on using pipes instead of full round bar? Those can be found in good precision, not always in size compatible with standard 20/25/30mm linear bearing size, like 1.5m long 22.5 (or is that 21.5?)mm diameter. There is one ball bearing based solution, I will take a photo. Not very easy to manufacture, however it could work out of 3d printer. I have a salvaged pair, its cast and machined aluminum - the machining is not very straight forward as it requires rotary indexed milling and drilling - not very possible for drill press only scenario. Could b e doable if one had a way to index the material for drilling and with crude angle grinder cutouts instead of milled slots. It also requires an eccentric element for play management.
Another idea to consider is round bar/tube which is preloaded - pulled on the ends. With pair of them and square tube or H-beam with brackets as structural beam between it could result in less sag than a rod/pipe just supported on ends. Anyone tried that?
Round bar has the advantage of easy solution for dirt scraper.
Last edit: 16 Mar 2019 13:20 by jmr.

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19 Mar 2019 12:48 #128966 by andypugh

jmr wrote: There are claims of belt drive being a good way. I know it can be used as a rack, this way teeth can be facing the bottom and would not collect the dust deposit,


The Bell-Everman "Servobelt" arrangement is good this way, the belt teeth are protected by the "counterbelt"

community.carbide3d.com/t/bell-everman-s...belt-system/10923/11 has a nice diagram.
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19 Mar 2019 13:28 #128968 by tommylight
Seen that when they started, it is a very nice way of removing belt flexing on machines and with light loads it can do some very fast moves. Planning to do that for a long time now, but time is not on my side.

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