As far as I can tell, the main purpose of the Metalmaslow top mount bar was the possibility that it would allow skipping custom calibration. If custom calibration is being done anyway, then any other 1.5" steel tubing of the same thickness should be just as good, no?
Does anyone know the thickness of the Metalmaslow bar?
Agreed. This is almost the same set up I’m considering, so it’s very nice to see someone already do it successfully, and in 2020.
I would be interested in hearing about what kind of accuracy you’re getting across the full sheet.
Thanks, Joe. I can pick up a 12’ long 1 3/4 x 7 1/4 LVL for about $35. So they’re not free, but I’d be glad to pay the money if the extra rigidity mades a difference. Any thoughts?
You are totally right, I misunderstood what you were referring to and had already edited my post after realizing what you meant. 12’ LVL does look like a good option!
Thanks. Looking at Jason’s pictures above, I was thinking a 12’ LVL would be reasonably close in size to the 2x4 plus metal bar that he used for the top rail. I’d probably go with the metal bar if one was available, but maybe the LVL would be a good substitute.
I love the level idea, and I think built the same way it would be just as stiff as the metal top bar. I would still try to have the original wood top beam and through-bolt the level to it to make absolutely sure it is rigid across the entire length. If the bar sags down in the middle, it can bounce and flex and reduce your accuracy. Remember you will also have 5-10 lbs of counterweights hanging off the unsupported center of the beam.
@joe_j I haven’t cut anything full span yet, the closest I have come is the calibration cuts which cut short lines in all four corners and they were all right where they were supposed to be. The large piece with the heart in the middle was 28" x 28" exactly as designed, and the photo cut-outs were exactly 5x7 so the pictures fit perfectly. I will have some larger projects that will truly test the limits soon, I will post back once I get them cut. For me, if I design it to a specific size and it cuts the material that size, I am happy. I also have to cut some 35.5" round frames which should tell me a lot. I will do them 2 up so it uses the entire sheet and we shall see if I have circles or ovals. The only problem with this test will be that it won’t be doing any cutting in the problem areas (top center and bottom corners).
I was expecting to be within 1.5mm or thereabouts, but my first cuts were right on the money. It pays to be accurate when constructing your frame, most important is that the sheet you are cutting and the top bar are perfectly level and that your chains are parallel to the work surface. If you nail those two items in construction and then measure very accurately during calibration you will be good.
I’ll be starting this project sometime in mid-May, once work tails off for the summer. Right now I’m just to figure out what’s what with Maslow.
My main projects for the summer will be outdoor furniture, and some repairs on a gazebo that we use during the summer. These projects don’t require high accuracy, but hopefully the CNC will allow a bit more design flexibility, and help with the repetitive work. Looking forward to giving this whirl.
Hi Jason - great posts and setup. Can you provide some more details on your counterbalance system for keeping chain tension? looks like you are going wit pulleys, what dimensions did you use, and how much weight on the ropes?
Good success cutting corner to corner?
Honestly, mine works but if I had it to do over again I would have re-thought the whole thing. I went for ease of setup, but that left me with my weights hanging down the center, right where all the wires converge. It has only happened once, but one of my weights caught on the signal wire for the Z-axis and worked it loose from the board. The Maslow finished the job, but the bit never changed depths again. Anytime the weights bump into something, you can see it in the piece. Only a slight deviation, but it is there (yes, I often watch that closely. LOL)
That being said, here are some things I have learned that might help you. Bigger pulleys are smoother, so I would use 4"-5" diameter at a minimum, and I would use as few as possible. The less drag on the pulley system the smoother the motion at the bit.
I would also rather have the weight lines route back out to the outside edges of the wasteboard, and run up and down out there where there is less chance for interference. My weights are about 5 lbs each, I started with 2.5 lbs but felt like there was too much slack. 5 lbs gave me good tension without putting any strain on anything, but that will vary by implementation.
The short story, counterweights are far superior to springs. Keep the weights running smoothly and out of the way and they will serve you well. There are a few threads around of people showing how they routed their weights to the outer legs. And my favorite piece of Maslow advice, don’t make it too hard. At the end of the day, most implementations will work well, and most will also require changes to get them “perfect” (perfect being a relative term here).
The only problem with this test will be that it won’t be doing any cutting in the problem areas (top center and bottom corners).