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  • wearymicrobe

    Oct. 21, 2010 6:18 p.m. wearymicrobe Reader

    Starting the bobber in the next couple weeks. I have been drawing out the bigger brackets out and converting them to DXF with solidworks and autocad. I will need to tweak them when I actually get the frame in and I can finalize the dimensions.

    So all I really need is +/- 0.3mm. Short of making it myself I kind of want to farm a bit of it out, specifically the parts that have variation in hole diameters across the piece . Does anybody know what I am going to pay approximately on the inch for a cut in 1/4 steel for water or plasma.

    I keep hearing plasma at 0.50$ a cut inch provided I supply the DXF and material. Does that sound about right. Waterjet seems to be much more but I have not seen any hard numbers.

  • 914Driver

    Oct. 21, 2010 7:34 p.m. 914Driver SuperDork

    You must be new, we're cheap bastards.

    What outcome do you want? Waterjet gjives something like a 125 or 250 finish, I don't know what a plasma cutter gives but I would assume either require further machining for fit & finish.

    Saw-Zall, die grinder, file, emery is free. If you have a blank check and can pay some guy in a garage, please call me.

    Sorry. I didn't answer your question, but I know alternatives.

    Dan

  • Oct. 21, 2010 8:31 p.m. kb58 Reader

    My only comment about plasma-cut parts is that the edges are crispied. What I mean is, they're burnt and oxidized, so if you plan to weld said parts together, you have to remove that scale... which makes the parts slightly smaller, if you care. For the stainless fuel tank parts I had made up, it kind of ruined the accuracy of the fit-up.

  • wearymicrobe

    Oct. 21, 2010 8:32 p.m. wearymicrobe Reader

    914Driver wrote:

    You must be new, we're cheap bastards.

    Saw-Zall, die grinder, file, emery is free. If you have a blank check and can pay some guy in a garage, please call me.

    Thats how I would normally do it but I want to build a seat post like this.

    http://www.flickr.com/photos/motormaniac/3835206665/in/set-72157621956362249/#/

    Its not something I can make. Should be pretty easy to have it cut. The fender brackets I drew up on emachineshop and it was ~145$ a side which is cheaper then I could ever do it if I had to buy 6-7 hole saws.

  • Streetwiseguy

    Oct. 21, 2010 8:33 p.m. Streetwiseguy HalfDork

    It probably depends on who and what is available near to you, and who is willing to do it without adding a PFO charge for dealing with small E36 M3.

  • Dr. Hess

    Oct. 21, 2010 8:41 p.m. Dr. Hess SuperDork

    The waterjet place I use charges by the hour of machine time. You give them your DXF, tell them what material you want and they run their time calculator program on it and give you a price. They have a plasma jet also and it goes through material faster than the waterjet, so it costs less to use. 1/3mm is pretty tight. You'll pay extra for that as the machine has to run slower. As I've said before, I use the chicken processing plant manufacturer. They specialize in stainless and were cheaper than emachine last time I had some stuff cut out. They also do a lot of granite countertops on the waterjet.

  • jamscal

    Oct. 21, 2010 9:36 p.m. jamscal Dork

    I can have them laser cut which is probably best for what they are.

    emachineshop is "neat" but too expensive.

    another alternative is posting an rfq over at practicalmachinist.com

    Finally, .3mm is too tight a tolerance for a seat bracket.

    -James

  • Wonkothesane

    Oct. 21, 2010 9:59 p.m. Wonkothesane Reader

    +- .3mm isn't bad at all, that's +-.012"! .024" of total tolerance is quite a bit! If your water jet can't hit that while running at a decent clip, I'd think you had problems.

    Plasma, on the other hand, will always need finish machine work to look acceptable, driving up the cost.

    I'd say stick with the waterjet.

  • Oct. 21, 2010 10:23 p.m. 93gsxturbo Reader

    ...laser. If its mild steel.

  • motomoron

    Oct. 21, 2010 11:00 p.m. motomoron HalfDork

    Most of the sheet metal fabs I deal with in the course of my day job (product design of large commercial scale solar electric mounting structures) use lasers. Tight tolerances are easily held w/ lasers, and water jets w/ kerf compensation can hold pretty tight on thicker stuff.

    I had some very swanky house numbers WJ cut out of .125" 304 SS by a friend's shop. I measured one before I tigged the studs on the back and it was within a couple thou. Amazing.

  • kreb

    Oct. 22, 2010 12:25 a.m. kreb Dork

    You can build a CNC plasma machine for under $10K.

    You can't touch a good water jet for under $100K

    Laser has similar quality characteristics to water, but costs similarly high and has a lower cutting rate.

    Just saying so people understand why the price differences. The comments about quality of cut are correct.

  • ValuePack

    Oct. 22, 2010 1:51 a.m. ValuePack HalfDork

    As someone whose overtime at an independent swiss shop is dictated by the demand for the name brand plasma cutter tips I make, I'd like my opinion to be a bit one sided... Truthfully:

    Do you want something you can pick up and start tacking it in? Waterjet. Mind waiting/paying for second ops, or willing/wanting to do the cleanup yourself? Plasma.

  • Zomby woof

    Oct. 22, 2010 6:08 a.m. Zomby woof Dork

    jamscal wrote:

    Finally, .3mm is too tight a tolerance for a seat bracket.

    It's not .3 mm, it's .6 mm

  • 914Driver

    Oct. 22, 2010 7:49 a.m. 914Driver SuperDork

    Weary, those seat posts can easily be made on a Bridgeport. I'm a handwheel & knob kinda guy, I don't speak CNC.

    Dan

 
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