circle issues

[mcmental]

morning all, just had a quick go at cutting a circle template out for my brother and well the circles aint really circular so im guessing i have settings wrong?
hypertherm 45xp using finecut consumables and settings from the book, 1.5mm stainless steel.
to stop the burn through do i need to make my lead in's longer?

[adbuch]

What kind of table are you using, and what software for your cam? Sheetcam or? What do the drop outs look like?
David

[robertspark]

if using sheetcam, set to pierce at the center of the hole for hole sizes less than 25mm dia.

The official line is to use a perpendicular lead in although I tend to use an arc leadin. it depends upon your machines acceleration and if you have a tunable G64 (blended motion) on your cnc controller (linuxcnc + uccnc have the options).

https://www.hypertherm.com/Download?fil ... &zip=False

https://www.plasmaspider.com/viewtopic. ... 72#p166326

[mcmental]

sorry, im using sheetcam and my software is commandcnc

[acourtjester]

When I look at you cut images is seems there may be some slippage in your drive system. The ends don't meet the start, see attached as to what I mean. This could also be caused by your table wobbling, is it a bolted together type??

cut part.JPG (97.24 KiB) Viewed 4798 times

cut part.JPG (97.24 KiB) Viewed 4798 times

[TJS]

As stated. Perpendicular lead in. I make them about .125" long or longer. I have no lead out on holes. Do not play with cut rules on Command CNC, they are built in. On thicker material you do want overburn I make the overburn about have the thickness of the material when using 1/4" or more. Slow the holes down to at least 50% of the book speed. Jim Colt wrote an article on holes on this forum and removing the divot. Make sure the gantry is square as well and your steps per rev are spot on.
T.J.

[SegoMan DeSigns]

I rule that works for me is a straight lead in to a straight line and an arc into a curved line. Also when your in SheetCam make sure the pause at end of cut is set at 0 as well.

[mcmental]

Thanks I’ll have a look through the settings and report back

[Joe Jones]

When I look at you cut images is seems there may be some slippage in your drive system. The ends don't meet the start, see attached as to what I mean. This could also be caused by your table wobbling, is it a bolted together type??
cut part.JPG

That was my first thought also. Either the table is not SQUARE square, or there is some slop in the X-Y mechanism, OR he could be using a full length machine torch and the torch is wobbling in the mount, allowing it to "cone" as it goes around the circle at a higher cut speed (G-forces).

The nick at the end of the lead in MIGHT be able to be reduced via corner acceleration. Perhaps the torch is spending too much time at the intersection? Cutting the amperage down a bit may also help.

I have a friend in Virginia who is also struggling with the shifted X start and finish points of a circle on a Samson 510 table. I might have to hop into my truck with the bin of spare parts and go see if we can isolate and fix the problem. Thankfully, my table has always cut round circles, so I cannot duplicate the problem here.

I want a LASER TABLE !!!

Joe



.

[adbuch]

Thanks I’ll have a look through the settings and report back

I will look forward to learning what you find out.
David

[ROKCRLER]

You didnt mention which table youre running, but for what its worth, I had similar circle cut issues, turns out my gantry got out of square, re-squared and now able to cut round holes down to .125 on .125 steel 45a regular consumables.
Im running a Dynatorch table.

[Joe Jones]

A gantry that is out of square may cause elliptical shaped holes, but that does not account for the inability to return to the starting point of a circle.

Joe



.

[ROKCRLER]

Joe, i agree.. again, without knowing which drive system were all ASSuming.
Mine was cutting semi circular holes and i did notice a bit of start/end point issues, PM'd the bearings, gantry and belts and back in business.
I'm definitely a newb, but i have learned to check mechanics before messing with settings. One thing I've noticed with new users (not saying OP is a new user) is folks, me included thought/think the tables are simply press go and done. Once i started religiously PMing the machine my cuts and consumable life have improved greatly.

I'll go back to my corner now

[mcmental]

I’ll have to wait a few days to report back as my ankle is not very happy!

[adbuch]

What table are you using? Some photos would be helpful.
David

[AJNess822]

For anyone opening this thread for answers I was having troubles with cutting perfectly round circles after a system upgrade, turned out to be EMI problems, Electro Magnetic Interference, from all of the wires, and possibly nearby welding machines etc.. I installed a grounding rod into the concrete and grounded both my plasma, Accumove, and table together and that alone made the world of difference. Other problems cutting circle are of course, play/wobble in any table components, bad consumables, out of square like previously mentioned.

[adbuch]

For anyone opening this thread for answers I was having troubles with cutting perfectly round circles after a system upgrade, turned out to be EMI problems, Electro Magnetic Interference, from all of the wires, and possibly nearby welding machines etc.. I installed a grounding rod into the concrete and grounded both my plasma, Accumove, and table together and that alone made the world of difference. Other problems cutting circle are of course, play/wobble in any table components, bad consumables, out of square like previously mentioned.