PS this is a thread about beam twist. You should start a new thread if you want to discuss torque.
4 Likes
You are right, sorry.
I think I’ll cut aluminum strut plates before the end of this week, and than make the deformation test for every strut configuration: no/HDF/ALU
2 Likes
It shouldn’t matter. It’s only a way to make the roller rise up. I think you could do it with a stack of shims, a 20 degree wedge, a doorstop, all sorts.
WOW that looks great! I can not wait to see it built
1 Like
That is THICK ning, bahahaha
Is that 1/4 inch
1 Like
Here
2 Likes
Looking sharp! no pun intended.
That’s not how I thought you’d end that.
No offense, but I don’t believe that number translates to the force on the belts of an LR4.
(Not my normal type of calculation…). Your number would be the force experienced by the cutting face of the endmill, most of which is rotational force which is dealt with by the motor and bearings in the router and acts against the long lever arms of the machine as a rotational torque on the router mounts. Very little of that is force acting against the belts in the X or Y axis of motion.
The force has to be traced back into the belts. If it wasn’t for the stepper motors, the router and cutter would be a wheel and try to roll away instead of cutting.
The belts are acting as the ‘hands’ which normally would be resisting the cutting forces on a trim router.
The cutting torque yes, but the cutting force should be the real force that the motors have to generate to move the tool inside the material, and to that you have to add friction and other load losses.
@vicious1 deformation test done:
The machine have a 1420mm Gantry, with 30x1.5mm steel tubes, all the Strut Plates are 5mm thick. No screws between Tubes and Braces
I physically locked the Y axis movement to exclude the belts’ elongation form the measurement, used a tube to let the cord slide on the bed, and used a Dyneema cord to connet the 45° Endmill to the 4kg weight:
RESULTS
- Without any Strut Plates:
2)HDF Plates:
- Aluminum Strut Plates:
Both Aluminum and HDF shows similar results, both close to 0.5mm, the aluminum ones reduce deformation to about 25%.
7 Likes
Nice test! I performed a test almost identical to yours, only with a 5kg load and on my full size lr3. I was waiting to finish my lr4 build and compare the test results. But I will quickly post my results to compare them against yours.
Setup was identical, y movement restricted, core in the middle of the beam and pulling on the collet nut. I just used a regular endmill and compared the back edge of the tool, tool stickout was 20mm. I screwed a block against the endmill and measured with calipers from there. This is more accurate then a ruler.
With a 5kg load I got a deflection of 1.33mm average on 3 pulls. This was on a full sheet lr3 with mdf struts. I did use pla plus on that build which is less stiff compared to normal pla.
My phone was flat during testing so I did not take pictures, see my sketch for the setup config
Also it is important to consider the tool stickout since this has a significant effect on the read deflection. It is better if we start using deflection angle to define the deflection, since it is independent on the tool length used during testing.
The angle is easy to calculate using Pythagoras or just use an online calculator.
2 Likes
That is great to see!!
What does this mean?
1 Like
The difference in beam deformation seem to be irrelevant between HDF or Alu plates with 4kg load.
The machine can’t lift that weight moving itself(with all values at 0.8A) so it will loose steps before reach 0.5mm deformation
I’ll perform the same cut done yesterday, and check if final dimensions are the same…
1 Like
24mm stickout, but Your math is wrong, for calculate the angle you need to know the exact pivot point, that’s not the router collet. So yes, the stickout is important, but not for what you mean.
The only thing we need is to know how much error the deformation will bring to our cuts, and a 20-30mm stickout is realistic.
1 Like
This also (as this thread does) assumes that deflection is solely a result of twist of the gantry and not bowing.
3 Likes
Exactly
Both good points which I did not consider.
1 Like