general questions for the experts and real world situations

[Graham Taylor]

Hi,

I have done the usual google searches to get an understanding of what exactly 'kerf' is with regards to laser cutters/engravers.

I realise that kerf is dependent upon the properties of the material being cut, the workpiece thickness, the lens focal length, and finally, the type of cutting gas used in the laser so what else can affect it? What else can affect it and how much do I need to be concerned (unless I am making boxes that need tight fitting joints)?


temperature/dampness of the material?
ambient conditions?
does the laser need to warm up during cold weather prior to 1st use that day to get an accurate cut or engrave?

What is the prefered air filtration system - does everyone use a filter or do people extract direct to outside? We are planning to extract the air directly outside as the back of our proposed new building faces the railway line and so no one walks past it etc.

I was thinking that I need a micrometer for getting an accurate measurement of the material thickness but what other handy tools would I need?

Hope the above make sense :confused:

cheers,

Graham

[Bert Kemp]

Graham,
I think if you can vent to the outside without bothering anyone else you should be fine in that respect.
Not sure what you mean buy letting laser warm up, I don't work in cold weather so maybe someone else can answer that, but I do let the water run about 5 min's then look at the tube to make sure there's no bubblies :D in the tube before starting to cut or engrave.
your other questions would depend on what you have for a laser, what materials your going to be working with and how precise you have to be.
I make a lot of boxes and as long as my laser is focused correctly the joints always fit snug.

[Graham Taylor]

we are getting a Trotec Speedy 300 and will be using mylar, laser rubber, paper/card and MDF.

[Mike Audleman]

I am fairly new too so might want to take all this with a grain of salt....

Download and cut this with each material and power setting you plan to cut with...
http://www.thingiverse.com/thing:84621

I have noticed that each combination of speed and power produce a slightly different kerf in each material. To be honest, its unlikely to be a factor unless you are needing +-1/1000th accuracy in your fit. And unless I deviate more than about 25% from my default settings for cutting, the kerf is MORE affected by focusing or lack there of than the power/speed settings.

Also the thickness of a material seems to affect the kerf. Thicker yielding a wider kerf. And I have noticed in these circumstances the kerf is not straight, at least on mine. Its tapered (wider at top, narrower at bottom). Matter? So far, no.

I vent directly outside. But its important to note that for every cubic foot of air you duct outside from your laser, one cubic foot of air has to come into the room from somewhere, usually from outside. In the winter, this may be an issue. I will be pushing warm air outside and by default a vaccume is being formed and will pull outside cold air in. I plan to build a filtering system to produce a closed loop system. This eliminates all the outside air infiltration issues.

As for tools....

Bought one of these:
http://www.harborfreight.com/9-1-2-half-inch-magnetic-parts-tray-with-hood-97801.html
I took the silly hood/rim off it. Its magnetic base is rubber coated and it sticks conveniently on my laser. It holds some postit pads, pen, pencil, fine point sharpie and a scalpel. It also holds some snippits of heavy aluminum foil, scissors, pair of hemostats and a pair of needle nose pliers. The scalpel is constantly used for picking out pieces from a sheet without moving the sheet (the fine blade slips into the kerf and easily picks out pieces). Also handy if you need to do any minor trimming where an incomplete cut occurred. The pliers are used for picking pieces out that fall down into the honeycomb as are the hemostats.

I scavenged several neodymium magnets from dead hard drives. I removed them from their metal mounts by bending the metal mount in a vice and popping the magnets loose with a screwdriver. One, I stuck onto the right sidewall inside the cutting area. I made a focus tool and put a small beaded chain (like the ones you find on dog tags or used to be in banks on their pens at the counter) through a hole on one end. The chain sticks easily and solidly to the magnet. This keeps the focus tool from walking off and its right there where I need it, in the cutting area.

I placed three more magnets on the front of the laser cutter (outside the cut bay). One I stuck a 16' tape measure to. I use that for gross measurements. The second holds my digital calipers used for measureing materials, objects and cut items. The last sits down low and holds a paint brush (the metal band round the bristles). The brush is for sweeping debris and refuse away from the cut pieces.

In a plastic tupperware style bin beside the laser cutter, I keep a Giottos Rocket Blaster, lens cotton swabs, microfiber lens cloth and a bottle of cleaning solution. These all stay inside the the bin where they are kept clean and dust free. This kit is used to clean the mirrors and lens in the laser.

I also have a few small clamps like this:
http://www.homedepot.com/p/DEWALT-12-in-Medium-Trigger-Clamp-DWHT83140/204389260
Mine are smaller though, think mine are 8 or 6". I use them from under the bed to hold sheets flat when the sheets are large enough to reach the edges. By clamping from under the bed, it keeps things out of the way of the laser head.

I also made some weights to hold stuff from scrap lead. I melted it and poured it into the bottom of soda cans to form small domes of lead with a flat base. They are thin enough so the laser head easily clears them when sitting on top of materials. You can see a couple of them along with a larger lead chunk (and boxes of bullets) being used to hold a slightly warped piece of ply flat:
http://www.wolfiesden.com/android/1024/2014-08-26_21-36-54_911.jpg

Also in the above image you can see some ultra-bright LED strip lighting I bought off ebay for around $15 for 5m of it. I lined all 4 sides of the bed with the lights. Though, hindsight tells me to only do the left/right and front and not do the back. Meh, its good and I can go in and cut it should I want to later. It really enhances the visibility inside the machine and is well worth the effort to add it to your machine.

[Rich Harman]

Download and cut this with each material and power setting you plan to cut with...
http://www.thingiverse.com/thing:84621


That kerf gage is neat in theory but you would be better off just using calipers. In order for that gage to work you need to cut both parts out of each thickness and type of material, and your edges need to be perfectly vertical.

I suggest that you not worry at all about kerf. When the occasion comes up that you need to compensate for kerf (if ever), deal with it then.

[Mike Audleman]

That kerf gage is neat in theory but you would be better off just using calipers. In order for that gage to work you need to cut both parts out of each thickness and type of material, and your edges need to be perfectly vertical.

I suggest that you not worry at all about kerf. When the occasion comes up that you need to compensate for kerf (if ever), deal with it then.

Well, thats exactly how its intended to work. Cut both pieces from whatever material/thickness you want to know the kerf of.

[Rich Harman]

Well, thats exactly how its intended to work. Cut both pieces from whatever material/thickness you want to know the kerf of.

Yeah, a bit wasteful. It could be redesigned so that the large piece is cut only once, then you just cut a small piece of each new material.

[Graham Taylor]

Thanks for the replies guys.

All points and suggestions taken on board - need to start planning room layout etc so I can hit the ground running.