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Thread: Another "which one?" question

  1. #16
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    I agree with Bill totally that holding down thin stock will be a dilemma. Obviously a vacuum hold down is going to fail on the wide open weave in the middle. As he said one catch and you will have a wadded up mess. Double sided tape might work. He's also correct that brass doesn't spark.

  2. #17
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    The solution for vacuum with things that will have open areas is a custom fixture which is very common for production type work on small things. You really cannot use a vacuum table like you can for sheet goods, both because of the open areas and because of how vacuum actually works for hold down. Strange as it may seem, it uses gravity which has something like the equivalent of 14 lbs per square inch. (don't quote me on the number, please, as this comment is more about the concept) So with small objects, there's not very much surface area to hold something flat and contained. Focused vacuum with a fixture designed for the purpose tends to be better for this kind of vacuum clamping because it can concentrate. It even uses a different kind of vacuum source than you would for a vacuum table.
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    The most expensive tool is the one you buy "cheaply" and often...

  3. #18
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    Jan 2018
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    "thin metal is very hard to hold securely"

    Yes. I planned to include tabs that can be cut off with a scroll saw then filed into oblivion. Would 4 tabs on the outer circle and 4 more on the inner be sufficient? 1/16"?

    I ordered some laser-cut blanks that had tabs of just 1/32", and it took 3-4 minutes of firm wiggling to weaken the first one enough to break. Scroll saw wouldn't work there because the kerf was too thin. Granted, there' no rotational force in a laser, but those tiny tabs were pretty strong.

  4. #19
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    Tabs are fine for keeping parts from flying, but you have to be able to keep the brass on the CNC table securely and perfectly (and I do mean perfectly) flat. That's where the decisions come around using double stick tape, using tape/superglue, using vacuum, etc., comes from.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #20
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    With what little I've done with brass sheet, blue tape and superglue worked fine. I did leave tabs in some non-critical dimension places, too, just to be cautious.

    John

  6. #21
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    If it was me, and I don't know if it would work without trying, is to get a sheet of 3/4" MDF (PVC would work if you want to use liquid cooling possibly) from the box store. Cut it 6" larger than the size of the brass you want to engrave. With CNC software you can design channels in it that will not line up with where your design will have the bit going. Make the channels at least 1/2" deep and not any wider than 1/2". Then drill a couple holes in the edge of the MDF for a pipe to slide in. Connect it to a vacuum pump and you'll have a hold down system. With 6" around the outside edge you can screw it down to the spoilboard. If you plan on doing multiples you could easily set up a way to align the brass to it and it to the CNC table. If needed the MDF could be doubled up by gluing two sheets together.

    I would use a dust shoe without any dust collection and possibly an air nozzle to blow the chips away from the tooling. The shoe should keep the chips from going everywhere. If you're worried about hot metal you could use an ash vacuum.

    I've never purposely milled metal on my 1F but I have hit the aluminum T tracks by mistake and it went right through it like butter. It didn't even make a different sound.

  7. #22
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    Comparison

    I compared Avid, OneFinity and Carbide machines. I'll try to attach the spreadsheet and would very much appreciate corrections of the things I mis-understood. But here's a summary of what I think I learned:

    Avid 4824 has a 2'x4' surface. There are a number of items you have to add, and there are 2-3 options for each. If you choose the least expensive options (including a router and NEMA 23 steppers), your cost is $7500. If you go to the highest options (with a spindle and NEMA 34 steppers), it's $10,700.

    OneFinity X-50 has a 32x48" surface, and can add sections of 2' indefinitely. It can't accept a spindle, (router only). But it can add a laser. Software is V-Carve Pro. Lowest cost $3600, high end is $4500.

    Carbide 3D has two models that define the middle- and high-cost choices. "Pro" and "HDM" have a 33x33" bed, and almost no additional costs. Pro uses a router and costs $2800. HDM uses a water-cooled spindle and costs $5400.

    Tolerances for all of these are about 5 thou. OneFinity's machine costs $1000 less than Carbide's. My current "hard questions":
    - is having a spindle worth $1000?
    - can a laser be bolted to a CNC even if the manufacturer didn't do it?
    Attached Files Attached Files

  8. #23
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    Attachment

    Trying again on that attachment.
    Attached Files Attached Files

  9. #24
    Whew! Things have gone up! Yes, you can add a laser to most machines. Might do some research on a particular machine. There are a couple of folks that sell a laser in kit form for the AVID. I have considered getting one (~$700 last time I looked?). Still considering... My experience with using the Bosch 1617 has been very favorable. No issues. I did add an aftermarket collet. If I could afford one, I'd add it, but the router is sufficient for my work.

    One other thing...don't forget to add in all the other stuff...tools, software, laptop for the machine(?), power strips, tables/bases, etc. etc. It adds up quickly! I think I almost doubled the machine cost buying all the other stuff.

    Yes, cutting brass is messy. I don't like to do it much. I had tiny little brass pieces everywhere when cutting, not so much when engraving (had to move the laptop way out of range!). I use no coolant. For holding the sheets down, I use screws, tape, super glue, etc. Lots of good methods out there. For cutting out shapes, I do make sure it is attached to the spoil board very well. So, even after gluing, I add screws in corners and such. I did use tabs for most of my work. For the tantalus hardware, I used glue and no tabs because the sides are beveled.

    I thought of something else I use my machine for a lot - layout sticks. Those little cheap engravers from eBay are great for marking up a piece with lines, points, crosshairs, etc. to use for layout. I also use those to engrave pertinent info on templates - dates, sizes, layout marks, centerlines, etc. Takes minutes and works great.

  10. #25
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    You can get a watercooled 2.2KW spindle for $400. I have the Huanyang 240V 2.2KW unit on my Onefinity. Love it.

    As Alex said, I like the ability to not have to use a computer to actually process the gcode and run the CNC. My design computer is upstairs in a bedroom, my Onefinity is in an external garage. Once powered up, I can transfer files via WiFi to the Onefinity controller, and remote start/stop the CNC carving on the Controller from either my upstairs bedroom or with my laptop sitting in my family room.

    I have a Nest camera, on the Onefinity, so when doing a long carve, I can see what the Onefinity is actually doing and also monitor the Controller, inside the house on my laptop.

    Following on from Alex's vacuum method. In the MDF, I would probably pocket out a recess that the plate could sit into.

  11. #26
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    At first I planned on double sided tape, but realized that even a small bow in the brass will affect depth of cut for fine lines. I can screw it down though the center, where a hole has to go for the clock hands. The corners are also available, because decorative cornices go on top.

    As for this fine lines, I heard a suggestion for a laser (another layer of cost and complexity for a new user). I also read about ‘diamond dragging”. I gather that’s a non-rotating stick with a sharp diamond on the end. The clocks get a small bit of Edwardian script, where a very fine line would be better than an end mill. I assume the laser burns away a tiny bit of wood. On brass sheet, does it melt it? Vaporize it?

  12. #27
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    I would find someone local that has a fiber laser. While I wouldn't try cutting out shapes with it, Your numbers will come out WAY better. And a 175mm lens and a 50watt would be good fit.
    Woodworking, Old Tools and Shooting
    Ray Fine RF-1390 Laser Ray Fine 20watt Fiber Laser
    SFX 50 Watt Fiber Laser
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    Powermatic 100-12 planer, Rockwell 15-126 radial drill press
    Rockwell 46-450 lathe, and 2 Walker Turner RA1100 radial saws
    Jet JWS18, bandsaw Carbide Create CNC, RIA 22TCM 1911s and others

  13. #28
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    Keep in mind that laser add ons are fine for light engraving work, particularly on wood, but they are low powered and not really good for any kind of cutting other than paper, etc. You also have to deal with the smoke produced. Anyone wanting to do serious laser work is going to be better served by a dedicated machine...but that comes at a cost.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  14. #29
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    Feb 2003
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    San Antonio, TX
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    One idea for holding thin metal I saw that seems to make sense is from the Woodsmith CNC Base Camp. In episode 006, Chris Fitch talks about metal inlays. What he does is use liquid hide glue to secure the sheet metal to an MDF backer. After all the machining is done, he places the back and the metal sandwich in a bucket of warm water for 24 hrs releasing the metal part.

    On my list to try. Just got the CNC almost assembled and will be making my first cuts this weekend.

    John

  15. #30
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    Dec 2007
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    Rochester NY
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    My experience:

    I make banjos, and I use my machine to cut pearl and wood veneer inlays, cut the pockets, and then scratch guide lines for hand engraving. Also cut fret slots in fingerboards and profile them. I have a tiny Techno Davinci router, 10" x 12" work envelope. It's 25yr old machine they made for educational use, but built as heavily and with the same quality & weight German components as used in their much larger machines. 1605 ball screws, precision linear ways, cast aluminum gantry sides, etc. It's amazingly accurate, I'd guess within .001", probably because it's so small and well made, nowhere to flex or rack. I replaced the controller, using Gecko 540 and Mach3 now, with original steppers and power source, not very advanced, but works just fine for me.

    I can cut out a complex shape inlay, and then cut the pocket with no clearance, then take succeeding cuts at .001" clearance intervals until it just squeezes in with no gaps. I use .012" end mills for tight points, it amazes me! I may some day get a larger machine, maybe 2' x 3', but I'd keep the Davinci for just this sort of precision work.

    My take is that if you need to do small, precise work, a smaller machine is going to be better. The Davinci's turn up on ebay etc for $1500 or way less, and it cost me less than $500 to redo the controller. You could also go with Clearpath servos and a better controller and have a fast, accurate tank of a machine.

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