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keelan
01-09-2009, 12:29 AM
I needed a threaded bushing for an old radial arm saw I am fixing up, and my metalworking machines are unavailable, and have been so for 8 years (sigh). I bit the bullet and took a quick drawing to a local machine shop. Here's a description:

.371" diameter, 1" long, threaded 5/16-18.

When they asked about tolerance, I said "it doesn't need to be super-accurate". I know that is vague, but I thought that they would make a reasonable attempt at getting it right.

To me, this seems like a very simple operation. $44 later, I have something that looks like it came out of a high school shop class on the first day of school. It serves my purposes, so I'm not going to bother with dickering with them, but I'm curious how a well established machine shop could produce such shoddy work.

The surface finish on the OD is far from clean, it has diagonal (helical, I suppose) sanding marks all over it. I can see where the three jaw chuck slipped on the finished OD of the bushing for about 1/4 of a revolution. One end of the OD is square, the other end is rounded over, and is visibly smaller than the rest of the bushing for about .1".

If you were to make a part like this in your shop, in what order would you do the 5 operations needed to create it?

pipeclay
01-09-2009, 12:39 AM
Would more than likely ,
1 Face
2 Centre drill
3 Drill tapping hole
4 Tap hole
5 Turn OD to length and Diameter
6 Part off
7 Return to chuck and Face and Chamfer one end Internal and External Chamfer
8 Reverse the job Face to length and Chamfer Internal and External diameters.
Around 20 mins work.

keelan
01-09-2009, 12:59 AM
Whoops, I forgot about center drilling in my count of 5.

And chamfering -- pfft, who needs nice edges? ;)

Couldn't one chamfering operation be done before parting the piece off?

Also, why part, rechuck then face to length, instead of parting to length?

I'm not challenging your answer, just curious about the reasoning.

tony ennis
01-09-2009, 01:01 AM
I would have tried something like this (4th item down) (http://www.fastenermart.com/html/500100000060.html). Costs a quarter plus shipping. Or $12 if they make you buy 50.

Then I'd turn round with a drill and file. I don't know if it would be 3/8" diameter or not. But a phone call would take care of that.

keelan
01-09-2009, 01:12 AM
Tony,

I realized this option on my way home tonight with my $44 bushing safely tucked away in my pocket. I was in the hardware store staring at the couplers, and it didn't click. Couldn't see the forest for the trees.

Oh well, live and learn. I suppose the correct way to look at this is that I supported a local business, and gave an apprentice some experience in how not to run a lathe.

dp
01-09-2009, 01:16 AM
Surely you told them it should be metal vs plastic, and suggested a finish? If you didn't specify finish then anything will do. The critical specified elements from you being the length, diameter, and thread based on your post.

Personally I would have had enough pride in what I do to have given it a decent finish, broken the edges, and ensured the diameter was coaxial with the threaded center though none of that was specified even if apparently expected.

Sometimes you just get what you ask for.

keelan
01-09-2009, 01:29 AM
dp,

When I talked to them, I specified steel, didn't matter what kind. I didn't specify surface finish, I had assumed that the part would come back as turned. At the very least, it shouldn't have had marks from where it spun in the chuck. You are correct, the critical elements were the dimensions specified. Concentricity of ID to OD, surface finish, and broken edges were all irrelevant, and therefore not specified.

I made the mistake of assuming that they might take some pride in their work, and produce something that at least looked reasonable.

tony ennis
01-09-2009, 01:32 AM
Personally I would have had enough pride in what I do to have given it a decent finish, broken the edges, and ensured the diameter was coaxial with the threaded center though none of that was specified even if apparently expected.

I rather thought that all that was standard. The finish should have been consistent, if not shining. The corners should have been eased, if not chamfered. I would expect the hole to be dead center.

dp
01-09-2009, 01:37 AM
I rather thought that all that was standard. The finish should have been consistent, if not shining. The corners should have been eased, if not chamfered. I would expect the hole to be dead center.

Ditto - but having read this BBS for some time I find that some folks will cut to the chase to save time which equals making money. I couldn't hand somebody something as described by the OP and expect to get paid, but then I'm a Unix guy, not a "real" machinist :D

Fasttrack
01-09-2009, 02:42 AM
Shoot - you should've posted it on here. I, for one, would've been happy to make the part for you. I'd probably even give a discount and only charge 30 dollars! ;) :D

Why don't you have access to your metalworking machines?

pipeclay
01-09-2009, 02:59 AM
Whoops, I forgot about center drilling in my count of 5.

And chamfering -- pfft, who needs nice edges? ;)

Couldn't one chamfering operation be done before parting the piece off?

Also, why part, rechuck then face to length, instead of parting to length?

I'm not challenging your answer, just curious about the reasoning.
Hello yes it should of been faced and chamfered prior to parting,I saw it but didnt bother to edit.

keelan
01-09-2009, 03:16 AM
Fasttrack,

I thought about posting here, but I didn't want to come off as a cheapskate. I'll keep you in mind for whatever breaks next ;)

Back in '98, my dad and I went half-n-half on a 3-in-1 machine, which we used in my parents front room for a while, long enough to realize that a 3-in-1 was a mistake. We sent it back,and upgraded to a 12x36 and one of those ubiquitous round column mills. Problem was there wasn't enough room in the house for them, and the shop was unheated. The plan was to tear out a couple unused bedrooms in the basement, and set them up down there. I ended up moving out in '00. My dad has since done the basement renos, but he has filled every last square inch with woodworking equipment.

So, the lathe and milling machine sit in the garage, packed in their protective goop -- they have never been uncrated.

I am now living in a town with ridiculous real estate prices, putting a place with a useable shop space well out of my budget. I live on a tiny lot with a rinky-dink 10x13 tin can shed that I keep a couple wood working tools in, but I wouldn't want to subject a piece of metal working equipment to those kind of conditions.

What bugs me the most is that even if I do set the machines up, at 8 hours away, my dad is too far away for hands on help. I wish I had realized the value of his knowledge and experience when I as younger and still living at home. He is "marine engineer", but since coming to Canada in the 60's, has worked on anything but boats. Metal working was a big part of his apprenticeship, and he's a great teacher.

winchman
01-09-2009, 05:15 AM
I'd go with the coupling nut, too.

Roger

Circlip
01-09-2009, 09:59 AM
Sorry, but it would have been back on the counter, a learning curve for the "Boy" not to produce crap, pride in work and all that. It ain't a case of being a "Moaner" no wonder manufacturing is going down the can. A classic NOT good enough.

Regards Ian.

Just thought, that equates to $450 an hour.

ERBenoit
01-09-2009, 11:00 AM
I'm curious how a well established machine shop could produce such shoddy work.

Well established machine shop, doesn't nesessarily mean quality machine shop. Just means that whatever they produce is apparenty "good enough" to everyone else to keep them in business.