Re: Runout on drill shank
1)
The motor shown, probably has no or low quality bearings. But for drilling (axial forces) it could work. Just give it a try.
If you use drills in a collet, you have to check if the drill diameter is stamped (bad) or laser engraved (ok).
You have to measure the runout of the chuck on the inside of the collet!
For PCB drilling, 0.11 mm runout is unacceptable (for me). Be sure to check if the chuck and collets are absolutely clean. It looks like the Chuck is heated to get it mounted. There could be some burned oil residues in the chuck.
There are no stupid questions, just stupid answers.
2)
Changing drills should not lead to a change in position. However, if If the drills are not the same height and there is no tool library, the Z position could be wrong.
3)
7kg.cm ok for positioning if the speed requests are low. You probably use Nema 17 motors. For the Z-axis you need some force to keep the drill drilling in stead of rubbing. But if speed isn't an issue, it could do especially if the PCB sizes are small. You could gear down to get more force. Keep the Z-axis weight low or add a contra weight.
There is nothing wrong with starting small and after a period of trial and error, learning, amazing and fun, you could go for larger steppers.
Re: Runout on drill shank
Hi Hfjbuis (glad I dont have to pronounce that :P),
Thanks for replying!
1)
Quote:
For PCB drilling, 0.11 mm runout is unacceptable (for me).
As a ball park figure ,what could be the allowable runout on the drill shank in your experience?
2)
Quote:
7kg.cm if ok for positioning if the speed requests are low. You probably use Nema 17 motors.
Yes ,I am using NEMA17,with a trapezoidal leadscrew with a dia of 8mm and lead of 8mm.The use these in 3D printers.The carriage weight for Y-Axis (moving gantry) is about 10kgs,driven by 2 leadscrews.The gantry is supported on linear bearing blocks.
I used the software mentioned here :
https://www.youtube.com/watch?v=22ZnBhxq6Yk&t=147s
I got 1.5 kg.cm for 500mm in 2 seconds.
Does that sound about right ?What do you think could be maximum speeds achievable ?
Re: Runout on drill shank
0.11mm runout is absolutely NOT acceptable. Try another collet if you have one. Make sure the collet is clean. Make sure the drill is inserted deep enough into the collet. Make sure the drill itself is not bent.
The machine itself should not lose its reference while changing tools. The mechanical force should be applied to the chuck, not to the machine frame.
But, in my experience, ER11 height repeatability could be as bad as 0.05mm or so. It's no big deal for PCB drilling, but for PCB routing I always touch off the tool after the tool change.
Re: Runout on drill shank
Quote:
I got 1.5 kg.cm for 500mm in 2 seconds.
Does that sound about right ?What do you think could be maximum speeds achievable ?
I have a small lathe. The Z-axis is driven by a 5 kg.cm nema17 stepper using a 1.5 mm pitch trapezoidal spindle. The weight of the carriage could be about 10 kg. I run it at 150 mm/min. I probably could run at 300 mm/min, not faster. The difference is that my carriage is pressed to the bed by pre-loaded ball bearings. This setup gives zero play but some friction. So it is not totally comparable to your setup.
Your calculations gives a speed of 15000 mm/min at a torque of 1.5 kg.cm. Your lead is 8 mm so the stepper should run at 1875 RPM producing this torque. The problem is that the higher the RPM, the lower the stepper torque. I thing you probably get 5% of the rated torque (0.35 kg.cm) and that isn't enough to achieve this speed. I guess you get 1500 mm/min.
Re: Runout on drill shank
Quote:
As a ball park figure ,what could be the allowable runout on the drill shank in your experience?
For me 0.05 mm runout is acceptable and "easy to do" on my small mill. I use an ER32 or ER25 (sort of) collet and drills with a 3.175 shank most of the time. For other types of drills i use a small drill chuck that has a 12 mm shank that fit's a collet.
More runout will produce to big holes and damages the pad around the hole witch makes it harder to solder and the structural strength of the pad is less.
High runout is an indication that something is wrong!
Re: Runout on drill shank
Hi,
I suspect that the run-out is excessive, I doubt for instance that spindle motor has bearings but rather has bushes.
With small diameter drills, say 0.6mm then run-out should be a small percentage of the diameter, 5% or less or the drill
will be short lived.
I would try what you have got, it may prove adequate....or it may not.....no harm in trying it to find out.
Craig
