Dross problems

[Wadzii]

I've got my machine dialed in pretty good on 3/16 mild steel.

My problem has come up going to 1/4" steel.

Using a hypertherm 45 on a homemade machine. On long straight cuts I can pretty much get those dross free. Where there is any sort of detail I get a ton of dross and there is always a little nub holding the material from falling out of the hole. I didnt have these problems with 3/16.

This is the back side of one of the parts. I've gone from 65 to 90 ipm with no real change as well and up and down on the torch height with no real change. (faster than 85ipm and there are areas it doesnt cut through)




In this picture you can see the nub at the start point. It does this if I use an arc or perpendicular lead in. Overcut is set to 0.250" and lead out has no effect on the nub..



This is another pic of the nub at the start point



Any ideas?

[sphurley]

Book on a 45 @1/4" is 60ipm? Why would you go faster and expect better results?

[Wadzii]

I tried 60 to as fast as it would cut. On 3/16 it looks the best at 95-100ipm

[Wadzii]

The dross comes off very easily so I assume that's low speed dross so I went faster. I'll try at 55 and see what happens

[sphurley]

I remember seeing Jim Colt mention moving where you put your lead ins at. The torch starts then you make it do a 90deg turn and it has to slow down causing the mark you see. Do you use any rules as you cut? Such as rules for holes at 60%? Using rules I can get most of my small holes (1/4") to be almost drill quality for size and taper. Also watch out if you use "soft pierce" in Sheetcam. If you don't have RS485 control to lower the current, SheetCam will still lower the Z down speed on pierce, then it's back to normal speed once forward motion starts.

[Wadzii]

I initially had a rule to cut small holes at 60% but the dross on the bottom was terrible, on the 3/16 plate there wasnt much difference between slowing down to 60% or running at 90%. on the pictures I posted I used a perpendicular lead in starting at the middle of the hole. I have a rule to slow down at sharp corners, not sure if I need to play with that.

I'm about to run a piece at 55ipm and see what happens. anywhere between the recommended speeds 60-75 look all the same. I havent seen an option for soft pierce so I assume I'm not using that?

[Wadzii]

I didnt get any pics, but I went slower instead of faster, the holes came out much nicer but there is still a good amount of dross on the back of the lettered areas.

[sphurley]

I would look at your letters (post the SVG or DXF here if you want) and see if you have a lot of small nodes instead of smooth flowing arcs.

[Wadzii]

I did have to smooth it all out when I first started with this part. The shop that was doing the laser cutting for me before originally drew the file and it had some odd things going on there.

I attached the file here.

[sphurley]

Back Plate Update.dxf

(49.89 KiB) Downloaded 74 times

Back Plate Update.dxf

(49.89 KiB) Downloaded 74 times

Your C's had some issues as did the bottom underline that was 4 separate vectors.
Not sure how much you think too much dross is. This was cut with a PM85's 45consumables (not the same as yours on a PM45)
I dropped it on the floor a couple of times and then knocked off the rest with a scrapper. An acid bath would have done everything in no time.
There is some taper in the corners of the letters as I would expect. You can play with the CV settings and get those even better at the sake of more dross.

[Wadzii]

the dross on the lettering was in huge globs. I just downloaded your modified file. I'll give that a shot and see what happens.

Let me know what you want for that plate. I can put it to use so it doesnt go in the scrap bin. Its the back plate for our cradle that mounts a ford differential into a honda s2000

http://centralncspeedshop.com/collectio ... kit-street

[sphurley]

You can have it. I'll ship it out to you tomorrow.
Steve