Anyone having serious bowing issues with plastics?

[Rodne Gold]

You can make a vac table cheaply - use a piece of aluminium , 1.6mm is fine thats drilled with 1mm holes spaced about 10mm (just less than 1/2") apart.
Anodised ally is even better - it absorbs the laser beam.
You can use 5-8mm perspex too but it will have to be replaced soon as the laser cuts into it. But you can prolly make the whole thing on your laser if you use perspex - including frame,
Make a wooden frame high enough to fit a vacuum cleaners pipe or use a reducer if you want to go thinner with the whole assembly.
Make a solid bottom and use silicon to glue top and bottom to the frame - seal edges
Find a way to get the pipe into the machine , buy a cheap vaccum cleaner, hook it up and hey presto.
Block off areas you arent covering with your material with card or photo paper for inceased vacuum on your workpiece
We also use a steel sheet and badge backing magnets if something is bowed. I only use the vaccum table for very thin stock like papers , some veneers and engravable self ahesive stuff.
If you make it too big or too thin in terms of top materials , the whole table bows in the centre
Use something under the table to make it level
Use your focus probe or tool to "clock" it up - run the laser head wth the probe or tool just skimming the table and you will soon spot where to lift it.

[Richard Rumancik]

. . . Find a way to get the pipe into the machine , buy a cheap vaccum cleaner, hook it up and hey presto.
Block off areas you arent covering with your material with card or photo paper for inceased vacuum on your workpiece. . .

If anyone wants to use a vacuum cleaner for a vacuum table, just be aware that vacuum cleaners were not meant to be run with the intake blocked off 100%. The air flows over the motor keeping it cool. If you have at least some leakage, it might cool the motor enough to keep it from smoking. The closer you approach zero airflow, the more risk of overheating the motor and maybe even causing a fire.

[Scott Shepherd]

Just got my batch in from Georgia. Bowed like a banana. The call is in to Rowmark for the next step.

Vacuum table doesn't solve the problem. When you finish engraving, you still have a bowed piece of material. I can't hand someone a new item I just made that's got a 1/4" bow in it. I don't need to pull the bow out, I need to GET the bow out!

[Scott Shepherd]

Johnson called back, all their material for this item is bowed at their location as well. They said they are unable to supply me with flat material in this product.

Well, that's reassuring. At least we've traced it to being bowed on their shelf and it's not a function of the shipping process.

[Dan Hintz]

And at least they were willing to admit it... too many companies would look at the product on the shelf (just the two ends of it touching, mind you) and say "Nothing wrong here, must be you!".

[Rodne Gold]

Good point there Richard , you need to block areas till your work is flat. If the vac starts whining and straining its too much.

[Scott Shepherd]

Rowmark called back too, said they would pull some stock from their plant and check it, and they would make sure I got some flat sheets sent.

[Dan Hintz]

<chuckle> They'll be flat when they leave the factory, but when they show up, well... :-p

[Joe Pelonio]

<chuckle> They'll be flat when they leave the factory, but when they show up, well... :-p

That's true too, I ordered from them in the summertime and found it warped from sitting all day in a hot UPS truck. That's when I found a local supplier in Seattle where I can pick it up. Trouble is the last batch from them was warped too as is all their latest shipment.

[Tim Baude]

Just got 10 sheets of IPI Engravers advantage. Use for trophy plates, plaque plates etc. They are the most bowed I have ever had. I will have some bowing, but not all the time. I am going to let JDS know....it is a pain to keep it flat for the cutting with the honeycomb table. Glad that I am not the only one to experience, but wish none of us had to.
Tim

[Bill Cunningham]

I haven't had a problem with new material, but once in a while I get a job where a lot of material has to be removed, so of course, the heat makes it warp. I keep my stuff flat during engraving by using a sheet of brass coated steel on the table, and the parts held flat with some 1/4" super magnets. I never cut all the way through ordinary 1/16 laser plastic, but rather just score it with the laser, and snap them cleanly apart afterwards. If I have to flatten a piece after engraving, I have a small drying oven, used for air flow heat drying water wash hard polymer printing plates. I run this at about 45deg C with a small weight on the piece for about 30 min, then turn off the oven, and let it cool..
Comes out dead flat

[Scott Shepherd]

Material just arrived from Rowmark. Dead flat, and I mean dead flat.

It was wrapped in plastic (like a poly bag).

Very good looking material. So it's apparently leaving the factory flat and it's not getting warped in transit, at least this piece didn't.

[Joe Pelonio]

Material just arrived from Rowmark. Dead flat, and I mean dead flat.

It was wrapped in plastic (like a poly bag).

Very good looking material. So it's apparently leaving the factory flat and it's not getting warped in transit, at least this piece didn't.

I have some arriving by UPS today too, I hope it's as flat as yours.

[Scott Shepherd]

One thing to note, the material I ordered was quarter sheets, the material Rowmark sent was full sheets. So the full sheet is dead flat. I would like to know if it's flat after it's sheared. The process of shearing it could be introducing stress into the material or it could be something else completely. But it's not too many steps between the full sheet and the quarter sheet and shipping them.

[Doug Griffith]

I suspect it's a process issue dealing with the differing coefficients of expansion of two materials bonded together.

I'd bet money Mike is correct on this. I'm surprised coextruding 2 dissimilar materials ever comes out flat.