I've also thinking about what to do for a bed with t-slots. My first thought was, like you, 20mm aluminium and machine channels into it. Then I saw the price of the piece of aluminium I'd need! It's probably the route I'll end up taking though as it's fairly simple.
The alternative option (which I've not priced up yet) is to get some aluminium profile, lay that on the bed so that it's very close to flat and then take a thin surfacing cut. You can then use the built in t-slots. Not sure how much cheaper that will be in the long run though. If you can get away with using regular or even thin walled profile I suspect it would be cheaper.
I've just about finished buying all the parts for my machine, cheap and simple are not available options
The DIYer biggest problem is that we never know what exactly the machine would be for, so we want it as multi functional as possible. At least that's me.
Originally Posted by Wobblycogs
For now the best i thought of would be to do the bed in the following manner:
Most of it Plywood with nuts covered by expanded PVC sheet 10mm, covered by another sacrificial sheet of the same material. The area near me/ the first square meter/, made with the thick alu channel extrusion + sacrificial PVC, or all same but holes left for a toolplate that can be bolted over all directly to the supporting beams. Or the first square meter made from square bars, cut and bolted so that emulate tool plate. Even if not perfect, they will be strong to bolt to and the plastic over them will be resurfaced. I even think that that type of machine could scratch steel, so i could resurface them directly.
After some thinking, calculating and so on, i believe i have the perfect compromise. Meaning- 1250x2500x200, very simple but robust Z, Z and gantry and bearings that will support the impact hammer. yes, i am still into the metal sheet forming idea. Atr least i would like to be able to try, without breaking the machine.
Basically with the design i achieved a 100mm/3kw/ spindle to have least possible overhang- the bit center from the gantry at ~ 80mm only. The spindle will be packed in aluminum rectangular of a kind. For the impact hammer a shell with the same dimension will be fashioned, so they could be easily interchanged.
I wanted roller blocks on the gantry and everywhere, but will be extremely expensive, and as i am not completely sure for the metal forming success, i decided on 2 roller rails +4 blocks on the Z and all else Hiwin 20 HG. For the sake of vibration and overbuilding i decided to put everywhere else 3 bearing blocks instead of 2. That will make everything rigid enough to withstand continuous vibration and at the end 4 blocks more from china will cost me only 150 euros more, which is irrelevant if the experiment succeeds or fails. having in mind that one roller blocks costs 100eu and 1 meter rail is double the HGR 20 rail price.
The roller blocks and rails for the gantry i found used for 150eu with shipping, so its a good deal.
Now the ball screw on the Z. Obviously with this extremely low overhang there is no place to fit the ball screw. So i fit it aside when i discarded the idea of third profile on the gantry, due to weight. So for the sake of vibrations of the impact hammer, i decided to fit 2 ballscrews. I believe even with one will work if not the hammer. As they are extremely cheap, i want just to be sure and overbuild here
What i want to say that if i had not made any big error, this design is quite sweet looking for a sturdy DIY machine.Take away the 3rd bearing blocks and the second ballscrews from the design/ due to the impact hammer/ and here you have quite simple but sturdy Z with only 80mm overhang to center of router bit from gantry. I am happy.
Any critique will be appreciated. Its not finished but i wanted to share.
PS. Dont worry for the holes placement and assembly, its under control :-) . Some minor changes will be made to the design so everything can fit in place without problems.
Last edited by Boyan Silyavski; 13-12-2013 at 09:30 PM.
Silyavski, I'm liking the Z design but I worry the whole thing will shake to pieces once the hammer gets going.
Last edited by EddyCurrent; 13-12-2013 at 09:40 PM.
I really hope it would work. If you knew how much time, money, effort, sacrifice and Love went to that project, you will understand why i will take the risque.
Originally Posted by EddyCurrent
If interested look here at this dissertation . I know it by heart of course, but from page 53 onward is the interesting stuff. On page 55 you can see what machine they used and later the tool and the result. I mean if they did it like this, i should be able to do it even better with mine.
I know you want a machine to do everything but I was thinking about this cheap 2 axis idea.
Hammer mounted in a steel frame, the hammer can pivot.
A linear actuator connected to the top of the hammer can pivot it to the required angle.
The base rotates under the hammer.
This is not the one I would use but is just an example
Last edited by EddyCurrent; 14-12-2013 at 01:54 PM.
The Following User Says Thank You to EddyCurrent For This Useful Post:
Originally Posted by EddyCurrent
This is a very fresh idea. I would say the best idea till now.
It still will have to have Z and rotating axis. But this great idea eliminates the gantry and bearings blocks there. It will be best to use screw jack servo motor or similar instead the actuator.
I see a lot of +++:
Only 2 cheap big bearings will support the Z, where the hammer is, the enclosed structure will be more rigid and so on....
It seems doable. I will start working on this design and definitely will bring it to life when i have the big CNC machine ready.
By the way i have my eyes on big THK steel slew ring roller bearings in ebay. For the shell mount rotation. Will dig deeper these days. They ask like 500eur for 60cm diameter bearing assembly which is incredibly cheap. Though the one that suits me seems not to have mounting holes for the actual ring. Will investigate further.
However the Big question for me here is - How i would control that thing? What software? This is quite unclear to me.
Just thinking very quickly about control, it may not be good enough for your requirement though. (trying to keep it cheap and simple)
The base would be a simple motor and gearbox
The screwjack would be simple motor operated.
The base would rotate at a constant speed.
At each full turn it will trigger a switch that will move the screwjack a small amount using a timer to run the motor.
2 limit switches will indicate when the hammer is at each end of it's travel.
There will be one motor that drives everything.
The base and screwjack are connected by belts and pulleys to provide the correct speeds.
As the base rotates the hammer will slowly spiral into the centre.
A VFD will control the screwjack
A simple motor will rotate the base
A tacho generator will be connected to the base so that it's output will be proportional to the rotation speed.
The output from the tacho will feed the reference (0 to 10v) of the VFD.
As the base rotates the hammer will move a small amount to spiral into the centre and if the base speed changes so will the screwjack speed.
Last edited by EddyCurrent; 14-12-2013 at 02:47 PM.
It should be programmable. There are certain moments that the hammer needs to spiral towards the center, otherwise waves of material rize due to accumulated tension and at a certain moment everything will wrap if not controlled.
Originally Posted by EddyCurrent
Mach3 can do 2 axis so G code could control it and now I've seen the power of Mach3 Brains there's all kinds of things you could do.
Last edited by EddyCurrent; 14-12-2013 at 04:15 PM.