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I am a student in the midst of building a cnc machine and would like to have 2 pipe rails drilled with 3/8" holes spaced at 4". I can do the layout work myself if this would help keep the cost down. I'm in the Southern California (Los Angeles or Orange County) area. The rails will most probably be either chrome plated closet-rod, stainless steel tubing, or polished black iron pipe.
I've attached a drawing for reference. Thank You.
Will you be providing the material? If so I can do this for you at $30.00 each plus the shipping.Quote:
Originally Posted by sonicwonder2000
If I am to provide the material, let me know what your prefer, and we can go from there, but I expect that you can add $15.00 ea. to the price. This is my first quote or post so I am not sure how this works.
Thanks,
Bill
Don't publicly quote your price. The low ball shops can look at your price and blindly bid $1 lower and you're out for no good reason. I'm not in the undercutting business, so it makes no difference to me.Quote:
Originally Posted by snedden4
I think you or anyone else will be VERY challenged to verify the specification "perpendicular within .020°", especially given the vagueness of the material specification. Is there a more measurable, forgiving way of communicating what you want there? I'm not going to give you a price, just observing.
Sure. The are going to be 4" long threaded rods placed in the holes and tightened with nuts against the inside and outside of the rails. These will serve as "rail standoffs". The rails will be mounted with these threaded rods on 1.5" square wall tubing that has been drilled with 1/2" holes.Quote:
Originally Posted by beege
All these threaded rods need to be in line with one another. I came up with .02 degree based on the fact that a .02 degree deviation over 4" will yeild a .001" tolerance at the end of the threaded rod (if my trig is correct)
Basically the holes need to be in line with each other to within .001" and drilled perpendicular to the pipe surface. Is this any clearer?
Good thing you're a student. Chances are with the spec that you've given above that the stud will have .005" clearance and never touch the pipe. Your contact is going to be the nut edges, and face. I'd specify "holes on center within .005", and you'd probably be just fine. Don't spec something you're not ready to measure yourself, and have a means of such measurement in mind. To ask for ± .020° in real world just increased your part cost (fixturing, measuring) by perhaps double.
Thank you for your input :D ! I am actually a computer science student so mechanical engineering is not my forte - your comments help immensely. I tried to do this myself with a bench drill press and a v-block, but I am afraid I am not much of a machinist. Do you have any idea of how long this type of a job would take a skilled machinist? That will give me some idea of what to expect in terms of a fair price.Quote:
Originally Posted by beege
Thanks again.
When you tighten the nuts on the allthread, the flats and points of the nuts will end up oriented in random positions and will likely tweak the surface of the tubing so much that ANY of your tolerance callouts are downright laughable. Then throw the possibility of the material being chrome closet rod, and this is a no-win job for any shop. Hell, just look up the manufacturing tolerances for any tubing and you'll quickly see how this entire part is headed down a bad road.
My suggestion to you is to explain what the part does (as you've allready done), and ask that the holes be placed as accurately as is conviniently possible. You'll get a lot more cooperation that way.
Just one more thing, the internal nuts will very likely deform the pipe by a fair bit unless you design in either washers with a curved base to match the internal pipe diameter or have the internal pipe diameter machined onto the bottom of the nuts.
Obviously the problems lessens as the wall thickness increases ie, the pipe gets stronger.
Good luck M
http://motionsystemdesign.com/msd_ne..._short_linear/
http://www.danahermotion.com/website...assemblies.php
Have a look at these. Perhaps you can get "linear guide rails" preassembled, and more precise than what you've spec'd here. You could probably get your 1 1/4" diameter, 4 feet long.
By the way, how did you plan on tightening the bolts two feet inside the tube?
Sorry for the late reply, I've been away for a couple of days. The nuts are very easy to tighten, actually. Just place the nut under the hole with a magnetic pointer and twirl the threaded stud until the nut threads itself. I've tried it; it works.Quote:
Originally Posted by beege
For everyone else who replied, thank you. I was able to find a shop locally that was able to do the work for me on my budget. I am afraid the commercial linear system rails were outside my budget or they would have been considered the the prime option from the get-go.
This RFQ is now closed.
You can orient the nuts in their proper position, then tighten up the "jam nut" on the bottom. Not hard to do at all with a stacked assembly like this. Or, a small half moon piece can be made to use as a "pad" on the ID of the pipe so the nut can have a flat area to tighten against.Quote:
Originally Posted by Matt@RFR