Engineers/drafters, need help with a print.
 

Below is a cut from a print (it's just a steel tube). But I cannot remember what the symbols "250<" on each end of the length are in reference to. Any ideas? My CAD guy is out and I'm trying to rush a quote through. Thanks
http://forums.pelicanparts.com/uploa...1176148609.jpg

It may be a surface finish callout. If so, it's pretty rough. It doesn't appear to be a geometric tolerance callout.

I also thought surface finish, but that doesn't make sense in the application.

A surface finish call-out would nomally look more like a check mark with a closed top on the bottom 'v' or a circle drawn in the bottom 'v' for an unmachined surface.
The V shown usually indicates a countersink on a hole, but on the ends of the tube? I would normally call that a chamfer, besides I can't figure what the 250 would mean?

Never seen such a symbol. You will probnably need to ask the customer to be very clear on what he wants.

Yep, but I wanted to double check that I wouldn't look completely incompetent for asking:D

surface quality.

basically, it needs to be cut to fit within the +/- tolerance listed

Length and angularity tolerances are listed separately.

I would guess '250' indicates this tube is connected on each end to another piece labeled as '250' on another drawing.

I also think I could make this piece with a hacksaw in my garage ..... :D

78,000 parts a year on this one, 570,000 on another length. The garage hacksaw gets tiresome at those EAU's:D

Or maybe not .......

250 is the finish in micro inches. 250 is pretty rough, like a phonograph record. Is it mating to a soft metal gasket?

Nope, it's actually just the center tube to an office chair.

But that isn't the standard symbol for surface finish!
If the correct symbol was being used one leg of the 'V' would be longer than the other.

As far as I know, a 'V' with equal sides is only used for a countersink in a hole call-out, or to specify a field weld as part of a welding call-out. Neither of these seem to be applicable in this application.

I suppose the only way you'll know for sure, as others have said, is to call up the supplier and ask him exactly what he means.

Lendaddy, I am 100% sure that is a finish mark. The larger the number, the rougher the surface can be. A 16 finish would pretty much require grinding to achieve while a 32 is typically a machined finish, 250 is pretty rough in comparison, but you might want to look it up in machinists handbook to be sure your cutting operation is good enough. (we seldom use finish mark numerical call outs where I work, so my memory of how "rough" a 250 finish can be is hazy).

For reference, that ground plate we made for you had a 16 or better finish on the large surfaces and a 32 or better finish on the machined cam track surfaces.

If you still need to know more, I will look in a machinist's handbook when I am back at work tomorrow morning.

Thanks Tim and everyone else, I'm going to get the scoop from my customer tomorrow.

We use surface finishes pretty regularly at our shop, so I'm with Tim on thinking this has to be a surface finish. A 250 turned finish would made with something like a 0.040" to 0.080" feed which is pretty fast. If they spec something that rough, it's usually because they want it made fast (ie cheap) or it's mating to a soft surface that they want to deform for a better seal.

This actually makes sense as they are currently being cut on a "Modern" which is a lathe style cutoff.

Here is a link to chart showing some various surface finishes that can be obtained with various processes. 250, while kind of crude, may be dicey depending on your tube shearing/cutting equipment, so it might be worth cutting a sample with your equipment to make sure it is acceptable. (I am a worry wart when it comes to making parts to other companies prints and getting burned down the road due to innapropriate or un-neccesarily tight tolerances)

http://icrank.com/cgi-bin/pageman/pageout.cgi?path=/data/surface_finish.htm&t=2

David, what do you do for a living?.....It seems like you and I often have similar responses to various mechanical/machining questions. ;)

I design custom automated machinery and we have a machine, shop, fab shop and controls department where I work. http://www.radcoindustries.com/

Funny, but a lot of newer CAD packages do not provide ASME or ANSI standard symbols in their default settings. Some cannot be customized to provide them, either. Part of the general shift towards sloppiness I have been seeing in this business for years. You certainly have a surface finish callout there, albeit a poor effort at one. These guys are right, too, in that 250 RHR can be achieved on the bandsaw. I won't even call them out when they are that rough unless, for some reason, it has to be that rough. That's seldom the case. Most applications I deal with are "or better" finishes, with the callout being the minumum acceptable finish.

It really defeats the object of having a standard if people won't/can't use them doesn't it?

While I can see that the INTENT may be for that marking to be a surface finish it isn't the accepted standard for a surface finish, so I would suggest the draughtsman would be better off just putting a note saying "Surface finish on ends of tube to be...." and eliminate the ambiguity.

I don't know if that's a surface mark. Looks more like a wall thickness value based on the ID and OD of the part. If it was a surface finish, the value would be a range, say "50-250 microinches." Even if it's a wall thickness, it's a poor method of indicating it.

Then again, I deal with large pipe and we don't particularly care so much about the finish of the cut, since we bevel and weld the ends together anyhow. 1.125" pipe/tube with 0.250" wall thickness is pretty hefty.

I rarely see drawings with indicated dimensions or surface finish that didn't have a unit of measure on it. I sure as hell try not to let something like that happen.....

It can't be a wall thickness as with an ID of an inch and and OD of and inch and a quater the wall would be an eigth.

Yep, wall is .125"

Yup! serves me right for typing on the BBS while working....and looking at piss poor drafting work! (sorry, I've been screaming at drafters the last few weeks to get ***** done....and correctly)

Jeff, this surprises me. Even my almost decade old copy of CADKEY 98 has these symbols available. Are you talking about low cost "consumer" CAD systems, or software that actual engineers would use?

Len, I really hope yours is the winning bid. (Can you actually find tubing/pipe with those OD/ID dimensional callouts, or will one or both diameters need to be turned? I don't have any of my material catalogs in front of me.)

Good luck,
Jim

Once again, it IS a finish mark and I and others have used that exact mark on mechanical drawings. I deal with drawings from many different industries including automotive and I have seen that often. another mark that is ocasionally used is one that looks kind of like an f hole on a violin only with sharp corners.

I'll agree with the others. It is surface roughness. It is a piss poor surface texture symbol, but commonly used. And it does mean 250 microinches, which is about the middle of the range of band saw cuts, so it means use a sharp blade with the right size teeth.

Yup...surface finish and he's going to seal on the end of the tube, so like Anton said don't hack it to length with a crap blade.

Just being pedantic, but what standard is that then?

Thanks Jim, and yes that's a very common size tube in either DOM or electric weld though the I.D./O.D. tolerances make DOM (Drawn Over Mandrel) the obvious choice.

Regarding end finish, we use cold saws and/or our orbital shear, both of which produce an excellent end finish, much superior to that of a high speed lathe cut-off.

I'm wondering now if this tube is involved in the pneumatic height adjustment and may actually need that soft seal. I'll find out today either way and post here if only for entertainment purposes. Thanks again guys.

I'm a mechanical engineer for a utility machine shop. We mainly repair turbines and pumps, but our main value comes when we have to reverse engineer a part that hasn't been made for many years and/or the lead time from the OEM is too long. Sometimes the OEM's even give us the original drawings if they know they can't fabricate the part as fast as we can.

It's probably not as interesting as designing new stuff like you do, but it's still pretty fun and it gives me access to machine tools to make Porsche parts and other racing stuff :D.