Plasma Cutter

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Re: Plasma Cutter

Postby mike » Wed May 16, 2012 2:38 pm

te_gui wrote:...how many folks were going to be at Maker Faire this weekend, and if any OrdBots were in attendance.


I'll be there with my ORDish bot -- Looking forward to meeting Bart and any buildlog folk who show up.

--Mike
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rack and pinion

Postby mikegreen » Wed May 16, 2012 4:08 pm

On the metric side, I have had good luck with the GEABB1.0-15-10-K-6.35 pinion from Misumi. It's very sturdy. I have mated this with the RGEA1.0-500-Z rack. The nice thing about the rack is that it can be ordered counterbored and fits very nicely onto the t-slot on the MakerSlide. There is a picture in the design ideas section. Since these can be ordered with machined ends, in theory they can be joined together for longer lengths. I have two mounted on MakerSlide, but I'm not sure what I think about that configuration. I can feel it when the pinion crosses the two racks. I need to do some measurements to see if this is a real problem or not. I can't find Module 1 rack longer than 1,000 mm (QTC gears has 1,000 mm without counterbores), which is a bit short for your purpose unless joining them together works out. M1.5 comes in longer lengths. I used M1to keep the width of the rack down to try not to have the carriage too far from the MakerSlide.

Thanks for the pictures. I was about to give up on the rack and pinion idea. In looking at the torque curve for the stepper motor that I have, I understood why direct drive was not going to be the best idea, at least for a router based system. I need to gear down to around 3:1, just like CNCRouterParts has done. Even without the gearing down and only using a 282 oz. stepper from Automation Technology, I agree that it's scary strong. More than I had expected, even at high speeds. I like how you handled the gear mounting. I was thinking of something more complicated and that was what was causing me to consider just going to lead screws for the x and y axis.

It will be interesting to see what you come up with for rack and pinion on the Z axis. I'm still working out the Z axis lead screw configuration for my experiment.
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Racks and pinions

Postby bdring » Wed May 16, 2012 4:27 pm

I know a lot of the MechMate router builders use racks from Standard Steel Specialty Co.

http://www.stdsteel.com/

I am waiting on quotes, but have heard some really good prices on their 73 inch racks.

I am using a 15 tooth gear now, I would like to find a cheap 20 tooth 24 pitch 14.5 P.A.
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"If you didn't build it, you will never own it."
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Racks and pinions

Postby mikegreen » Wed May 16, 2012 4:52 pm

It will be interesting to see what you find. Cost is an issue with the options that I listed (~$100 USD per 1,000mm for rack). By the way: I just checked, and Misumi does have 980mm M1 counterbored rack if anyone is interested. Not sure why I missed that before. It's just a few more dollars more expensive than the 1,000mm rack without counterbores from QTC gears, but the machining on the ends is different for the two products.

I have been looking at some of the discussions related to MakerSlide and flexing at longer distances. I have not done any tests like I have seen posted, but I wonder how mounting steel counterbored rack to the side of the MakerSlide extrusion affects the flex. Having two 500mm sections of rack mounted onto the t-slot in the MakerSlide certainly appears more sturdy. That's one of the reasons that I did not want to give up on an R&P design.
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Re: Plasma Cutter

Postby diane-mooregear » Thu May 17, 2012 3:08 pm

We manufacture and sell gear rack commonly used in cnc routers/plasma cutters and other rack and pinion devices as a stock item and regularly sell these in small quantities to independent builders.

If you have any questions or would like a quote, I welcome inquiries at diane@mooregear.com. We accept credit cards and ship domestically and overseas.
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X Z Carriage

Postby bdring » Thu May 17, 2012 5:42 pm

Here is what I have for the X/Z carriage so far. I do not need much Z movement, but it is nice to have a few extra inches or it can get whacked while loading stock.

I have Moore Gear quoting me some racks. I will post the details. Thanks Diane.

rd_z.jpg
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Rack Price

Postby bdring » Wed May 23, 2012 2:33 pm

I got a quote back from Moore Gear for racks. The quote was for (2) 6' foot 20 pitch racks. The racks are 0.50 square, which is wider than will fit with my eccentric spacers but it is probably only a minor modification.

The cost is $113 delivered.
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Re: Plasma Cutter

Postby gavztheouch » Wed May 23, 2012 10:20 pm

Nice project! Is your spur gear preloaded/sprung against the rack?
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Re: Plasma Cutter

Postby bdring » Wed May 23, 2012 10:48 pm

The entire stepper/gear assembly rotates into the rack. It has provisions for spring loading, but right now I am simply bolting it in position. I need to get a feel to the tension I would use.
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Frame Parts Ordered

Postby bdring » Fri May 25, 2012 4:29 pm

I ordered enough parts to begin testing the basic mechanical platform for the plasma cutter. I am going to limit the size to 24" x 48" (work area) for now. The primary thing I am worried about is strength of the gantry. That is being built full size. The rest is scaled back. My biggest concern is twist of the gantry. It did some experiments with some MakerSlide of that length that look promising, but I need to get a real feel for it.

I might need to double up on some of the corner brackets, but it would be nice it would be able to cut well enough where it would be able to make its own extra strength brackets and plates. I will also add some feet or wheels to the design.

Usually the work surface needs to be replaced on a regular basis, so it is designed such that the cutter can make it's own "consumable" parts.

I will probably use cable carriers, but I want to investigate a simpler overhead arm type like you see on "Plasma CAM" type machines.

The final design will incorporate a water table or down draft system to cut down on the smoke. I talked to many people at Maker Faire about that and they all liked the water table method the best.

plas_09.jpg

plas_10.jpg
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