Rough Edges

[farmer53]

Hi
I have what I would call a saw tooth look on the edges of my cuts. I have seen cuts that look perfectly smooth but I am unable to get mine to look like that.

I am presently cutting 14 gauge with fine cut consumables. I am using a hypertherm 600 with a RT60 machine torch. I have a Dyna CNC table with servo motors and a MP 1000 torch height control. The edges don?t have sharp edges but are rough to the touch and rough in appreance.

I have tried cutting with THC both on and off. I have been cutting some pieces with a lot of fine detail so I have my travel speed set at 100 ipm. If I set the speed up higher it gets real jerky because of all the short moves because of all the detail.

I get a lot of dross but I think it is because of slow travel speed. Most of it comes of easy with a 2-? inch wire brush. I am also now cutting over a water table.

I am using corel draw with DXF format. My CAM program is Sheet Cam and the software running the table is Mach3.

When I put my hand on the gantry the longer curves and straight lines feel like the gantry is moving smooth.

If I uploaded this right there are two pictures showing the edge.

Any suggestions would be appreciated.

Thanks

[elkriverfab]

Farmer53,

This may not be your issue but I have had the same problem in the past when cutting drawings that were just not drawn with very much quality.

Mainly files I purchased off of ebay when I first got my table years ago (bad lines).
I had to redraw them if I wanted them to cut nice.

I eventually just scrapped all the files I bought off of that place, just too much trouble.
They were junk and I guess that is part of the learning curve

Like I said, may not be the case with you but it can happen if they are not smooth drawings.

Have you tried other files with better luck?

[WSS]

Can you see how the line in the picture is drawn in a cad reader? Looks like starts and stops or many lines.

WSS

[farmer53]

Thank you for your reply.

Some of the files I have cut were from Cascade Metals and there are some simple files I made my self. I say simple because I am not very artistic. I have gone through some of them and removed as many nodes as I could without altering the basic shape to much. That seamed to help some but some straight lines that were cut as part of a coat rack yesterday still had the same problem.

As the straight lines were being cut I watched the x and y axis on the screen. Even the lines cut on the x axis that showed no movement in the y axis ( I assumed they were perfectly straight ) had the same appearance. I spoke with a local guy from Praxair today and he couldn't give me a good answer.

Thanks Again
farmer53

[WSS]

Ok, so if we assume the drawings are good ( I read you removed some nodes), Jasons drawings are pretty nice files usually needing only some nudging to squeeze a kerf line in, Is your shield dragging in any way? Maybe the arc volts could be raised to see if that changes the outcome. Or.....try the file on a different spot on the table. Could be a rough spot cuasing the motor to strain. Does it seem to be on just one axis, I notice you mentioned your y axis?

WSS

[ronsii]

Make sure your support slats are solid and you material is not able to move even the slightest amount otherwise you will get cuts like this mainly when the torch is not moving in just one axis ie. if one of your motors is stepping even just one pulse for the other axis travel of an inch or more you will get a jiggle or bounce effect on the material.

An easy way to test for this is to code in a straight cut 0,0 to 5,0 and 0,0 to 0,5 and see if the problem still exists.

[farmer53]

Hi
Thank you for your reply. I used a 4 foot X 8 foot sheet and it cuts the same from one end to the other. I'll try putting some heavy blocks on the sheet to maybe hold it from moving. I''ll also try what you suggested and cut a straight line by itself to keep the sheet from having a chance of moving.

I also spoke with a local guy that has a small torch mate table. I am going to try one of his files next week and he is going to try one of mine to make sure its not in the file.

I hope you are right and it is in the metal wiggling. I hadn't thought of that. This is all new to me. until late last year I had never been around this kind of equipment and had no idea what all was involved.

Thanks again for you help

farmer53

[AnotherDano]

I'm having a hard time picturing 14ga metal moving on the table. Especially a 4x8 sheet.
Is the cutting head secured firmly with no wiggle room?
This seems odd.

[ronsii]

I should have added what AnotherDano said about it could also be the torch or part of the machine with slop I also just noticed that you were using servo motors don't know why I didn't see that earlier... it could also be a loose/bad encoder on a servo but this would only show up in one axis and in your pics it mainly appears to be in the horizontal lines Does it do this completely around a circle cut?

[WSS]

I'm having a hard time picturing 14ga metal moving on the table. Especially a 4x8 sheet.
Is the cutting head secured firmly with no wiggle room?
This seems odd.

I can move 1" plate with one finger on my table if I do not clean the slat tops and miss a piece stuck to the top. When that happens I use a short piece of angle iron and clamp with two vise-grips and don't do any part retrieval or messing around the the table just in case it still wants to shimmy. It is a pain but shifting a 1" plate on and off the table is worse.

WSS

[Dennis]

Looks to me like a lttle play in the gantry..

[farmer53]

Hi Again

On my way back from the city today I stopped by the farm and made a single straight cut on the X axis and a single straight cut on the Y axis They were both a 100 percent better than when I ran a complete file.

When I looked over the gantry I did find a very small amount of in the Y axis where a gear is slid over a key stock and a little more on the X axis.

The way I have the slats in the water table they do wobble a little side to side at the end of the table. I plan to change the drive gear on the X axis next week as soon as I can get a new gear broached and put some loctite on the key way of the Y axis. I will also shim up the slats so they don?t wobble.

I think I will also try a few different settings for acceleration and see if I can get the gantry to move with less jerkyness.

After making the changes next week I?ll try a complete file but it is looking like these things are the problem. The looseness is so slight that I never considered it to be the problem so I feel pretty dumb.

I would like to share a couple of the files I made for a tractor but I didn?t actually draw them. I traced the outline of them from a picture using corel draw then added the detail where I thought it would look ok. From some of the posts I have read in the past I was afraid that if I didn?t actually draw it that it would offend others.

THANKS to every one for your suggestions hopefully they have helped solve the problem. I?ll find out next week.

farmer53

[AnotherDano]

I would like to share a couple of the files I made for a tractor but I didn?t actually draw them. I traced the outline of them from a picture using corel draw then added the detail where I thought it would look ok. From some of the posts I have read in the past I was afraid that if I didn?t actually draw it that it would offend others.

THANKS to every one for your suggestions hopefully they have helped solve the problem. I?ll find out next week.

farmer53

Post it!
Glad things are looking better for ya.

[evoandyvii]

Had similar problems on my water table for a retarded long time couldn't figure out why the cuts would walk and be jagged... about two months ago found out on the y-axis servo the set screw for the gear was loose... I suggest going around the table and tightening all the set screws on the servos.



good luck.