When to slow down?

[davek0974]

I keep reading that for good holes, speed should be reduced.

Trouble is, the reductions mentioned vary from 40 to 70% but no mention of what size hole this should come into effect?

I have a hypertherm 30xp on a small table, my main material range is 1.5 to 7mm.

[wilber]

I have heard Jim Colt talk about 60%. I am not sure on the math factor to get that percent.

[davek0974]

Yes I've read that too, but what size hole do we need to slow for?

10mm, 20mm, 50mm???

[rikduk]

Its always diameter of hole vs thickness.
You will rarely see good results below a ratio of 1:1 (7mm hole in 7 mm plate)
Its 50-60% speed on a 1:1 to 1.5:1 hole, after that, you increase speed gradually with hole diameter untill around 4:1.
So for a 12mm hole, youre gonna slow down in 7mm plate, but not in 1mm sheet.
You might have to experiment on this to find the best results.
We dont go slower, because it gets hard on consumables.

[jimcolt]

It really depends on the whole machine you have....cnc machine, acceleration rate, height control accuracy and plasma...they all work together to cut your parts. My rule of thumb is 60% of programmed "book" speed on all holes under 1" diameter. Larger than 1" makes it easier for the machine and plasma arc to deal with the left turn and the lag in the plasma jet.

Jim Colt

[davek0974]

Thanks all, the 1" circle raised a thought.

Today I was cutting a little job, it had some text on it and therefore a lot of curves etc.

Should these also have a reduction ?

Some of them were pretty much semicircles or more so I'm guessing they should be treated the same as small circles?

I think these could be handled with sheetcams' "shapes" cut rule.



I'm slowly beginning to see that there is lot more thought goes into a job before it even gets near the table

[TWSalaska]

I go to about 60% and then adjust from there... Its best to Do some test before you actually make the part.