[onocyclone]

Yes I've tested it when you reverse the direction. Spot on. Maybe 0.00001 out. It goes slightly past zero sometimes .

[photomankc]

The best thing you can do is post a video of your process on determining backlash so it is clear what is and is not going on and what and how you've tested.. If you are able to reverse with complete perfection then your part should be on-dimension within the limits of the machine's rigidity, tool flex, and real tool dimensions. That would lead me to suspect the program.

[onocyclone]

I'll have a look at it in the next few days,

[onocyclone]

What is the best accuracy that these machines can achieve ? With my ball screws ? (C7) 0.005mm ?

[pippin88]

Haha, push on the spindle sideways lightly and it'll move 10 times that.

[onocyclone]

Really !!

[SCzEngrgGroup]

On a benchtop machine, you're lucky if you get +/-0.003" true accuracy when actually cutting metal. The machine itself will move and flex quite a bit. The more aggressive the cut, the more error you'll see. A "static" test, measuring move distance while "air-cutting" is fine for confirming axis scaling and backlash, but tells you nothing at all about the true dynamic performance.

Regards,
Ray L.

[photomankc]

I'll second that. There are two accuracy expectations. There is what the machine can do with an empty table which ought to be very close to whatever the screws are capable of giving you plus any 'sticktion' error from the dovetails not immediately moving in tiny increments. That is interesting as Ray said for getting the axis setup, testing large arcs, and getting backlash adjusted and all. When it comes time to cut metal the machine is going to flex and there will be way more error than that static test would indicate. Even the tool itself will flex in a heavy cut.

That's where the use of roughing clearance and light finish passes do wonders. I can generally feel confident to promise +/- 0.0025" if I don't want to do any special setup or compensation. I can do better if I run a test or two and adjust the code to compensate for the results. Then I've been able to run small batches in the center of the table and get +/- 0.00075" on the X/Y. Z is always my most difficult to manage. Heat & spindle growth, touch-off accuracy, and accurate measurement of the tool length all make that a harder prospect for me to get better than +/-0.003" with.

[onocyclone]

Still not bad what is THE BEST couplers to buy then. No messing now

[photomankc]

Tough to beat Oldham couplers. Reliable, no backlash, simple, and tolerate massive alignment errors with no stress. They are even easy to make.

[onocyclone]

I can't see that if I made some solid couplers they would break the shafts. It would completely eliminate backlash as there is nothing that can move.

If I made them with 2 grub screws then it will be solid

[onocyclone]

The motors should stalk before any braking occurs. If you crash it.

[SCzEngrgGroup]

If the two shafts are not aligned absolutely perfectly - exactly on-center, and exactly parallel - one, or both, of them WILL eventually fatigue and break. It may take a few weeks, it may take a year, but it will happen. The chances of having them aligned perfectly enough to prevent this is pretty close to zero.

Regards,
Ray L.

[LeeWay]

I snapped one off myself this way. Since then I have replaced all my couplers with Oldhams.

[tjschweizer]

Onocyclone, your inbox is full so I couldn't send a PM

[onocyclone]

Try that mate.

[onocyclone]

Ive been messing with the machine again today, Ive re calibrated the machine and found that the head was not perfectly trammed. I need to correct this first. Ive been using a DTI to calibrate the machine and converted the imperial units on the DTI to mm. I got it so it was reasonably good but i then used a metric digital vernier scale and it shown it was extremely out. Like 0.75mm. I then calibrated the machine to the vernier scale and have got it to within 0.01-0.025mm.

Im going to purchase a higher accuracy digital indicator before i recalibrate it again.

Next thing I'm going to do is make some solid couplers and see if they will fix the back lash issue.

One point i must add is i tested the rigidity of the machine and i forced the table and it moved the indicator around 0.0005". Is this acceptable ?

Ive also messed with the velocity so i have got 800mm/Min in X
600 in Y
800 in Z

Much faster than before Haha, ill have to be more careful now, before i could go for a cup of coffee before it reached where i told it to go

[Fastest1]

Go ahead and start the thread, "why is the shaft broken"? At least you are consistent on ignoring good advice.

[arizonavideo]

If thy don't break the real problem is the vibration from the steppers making the ball screw ring.

[onocyclone]

Ok as everyone is suggesting i don't use solid couplers i will get these Oldham Couplers. I didn't mean to disregard peoples experience.

Where is the best place to get these couplers in the uk ?

My Ball screw ends are 3/8" ( 9.52mm )

Ive found that i can only get 8mm-12mm.

My Z motor has a 14mm shaft but can't find an oldham coupler this size ??

BG19-T | Ondrives


Cheers,


Olly