[sansbury]

I rent a corner of a shared space in Boston, and my new next-door neighbor is working on commercializing his Ph.D. research in robotics, which works out well for both of us because he has a low-cost machine shop nearby, and I have a small but steady customer with very low shipping costs and reasonable expectations. He recently asked me if I could machine some pneumatic fittings for him, real simple job drilling and tapping three 1/8-28 BSPP holes on alternate sides of a quick-release fitting just like you have on your compressor to make a manifold of sorts. The first couple I did more or less manually in a vise and hand tapping because he needed them yesterday, but he wanted about 20 more done and said I could take my time with those so I decided to see how to do them more efficiently.

Putting them in the rotary table seemed like an obvious choice since that would allow me to do all three holes in one setup. Normally I like to fixture more than one part at a time, but I didn't have a whole lot of brilliant ideas for this one. The round surfaces are all larger in diameter and either move or are too small to clamp onto, so it seemed like any kind of multi-part fixture would involve a decent amount of material and engineering, too much to recover in 15-20 pieces. The rotary fixture I made was a simple doohickey that had a 1/2" section I could hold in a collet in the rotab, a couple inches to provide clearance, and a tapped hole the fitting could screw into. I counterbored about .050" of the hole so that the fitting's shoulder would seat firmly against the fixture to keep everything square. Since all I had to do was drill and tap, I thought I could get away without the part spinning and loosening itself.

The second nut I had to crack was that the tap had a .435" shank, and I have an ER-16 tap holder which maxes out at .375". Back to the lathe for another little piece of 6061 with a .375" shaft and a .435 bored hole. I added a set screw to clamp against the square part of the tap shank. It wasn't the prettiest thing but I figured at 500 RPM it wouldn't fly apart and the holes were very shallow so the torque requirement was low.

The one shortcoming of the fixture I made was that I had to align each part individually since the threads didn't align with the faces of the hex section the same way from one part to another. So basically after screwing a part in and tightening it, I used a dial indicator to align the face perpendicular to the mill. At first this was slow, but after a couple I was able to do it in under a minute. I would jog the indicator down so it was contacting one edge of the face, zero it, jog to the other edge of the face, and note the difference (say .010"). I'd jog the rotary until the difference was .005", and then jog to the other edge, lather rinse repeat. Usually one or two passes was enough. Then I would zero the A axis and start the program. However, I made another change because a couple times I indicated the part, but forgot to zero the A axis. Then as soon as I hit run I'd watch the table spin back to the old zero and I just wasted a minute. So I added a line to the program that zeroed the A axis before it started, so now all I had to do was indicate the part and hit go.

By the time I finished I was averaging a little under 5 minutes each, so at $5 each with customer-supplied material and tools it slightly exceeded the $50/hr machine time goal I aim for. Setup and fixture/doohickey-making took about an hour and a half mostly because i just got a new lathe and I still don't have all the tooling for that set up well, so I had to do some workarounds.

[anglin]

Fixturing seems to be at least 75% of any machining task. Thanks for sharing your work and expanding my horizon.

[Steve Seebold]

I rent a corner of a shared space in Boston, and my new next-door neighbor is working on commercializing his Ph.D. research in robotics, which works out well for both of us because he has a low-cost machine shop nearby, and I have a small but steady customer with very low shipping costs and reasonable expectations. He recently asked me if I could machine some pneumatic fittings for him, real simple job drilling and tapping three 1/8-28 BSPP holes on alternate sides of a quick-release fitting just like you have on your compressor to make a manifold of sorts. The first couple I did more or less manually in a vise and hand tapping because he needed them yesterday, but he wanted about 20 more done and said I could take my time with those so I decided to see how to do them more efficiently.

Putting them in the rotary table seemed like an obvious choice since that would allow me to do all three holes in one setup. Normally I like to fixture more than one part at a time, but I didn't have a whole lot of brilliant ideas for this one. The round surfaces are all larger in diameter and either move or are too small to clamp onto, so it seemed like any kind of multi-part fixture would involve a decent amount of material and engineering, too much to recover in 15-20 pieces. The rotary fixture I made was a simple doohickey that had a 1/2" section I could hold in a collet in the rotab, a couple inches to provide clearance, and a tapped hole the fitting could screw into. I counterbored about .050" of the hole so that the fitting's shoulder would seat firmly against the fixture to keep everything square. Since all I had to do was drill and tap, I thought I could get away without the part spinning and loosening itself.

The second nut I had to crack was that the tap had a .435" shank, and I have an ER-16 tap holder which maxes out at .375". Back to the lathe for another little piece of 6061 with a .375" shaft and a .435 bored hole. I added a set screw to clamp against the square part of the tap shank. It wasn't the prettiest thing but I figured at 500 RPM it wouldn't fly apart and the holes were very shallow so the torque requirement was low.

The one shortcoming of the fixture I made was that I had to align each part individually since the threads didn't align with the faces of the hex section the same way from one part to another. So basically after screwing a part in and tightening it, I used a dial indicator to align the face perpendicular to the mill. At first this was slow, but after a couple I was able to do it in under a minute. I would jog the indicator down so it was contacting one edge of the face, zero it, jog to the other edge of the face, and note the difference (say .010"). I'd jog the rotary until the difference was .005", and then jog to the other edge, lather rinse repeat. Usually one or two passes was enough. Then I would zero the A axis and start the program. However, I made another change because a couple times I indicated the part, but forgot to zero the A axis. Then as soon as I hit run I'd watch the table spin back to the old zero and I just wasted a minute. So I added a line to the program that zeroed the A axis before it started, so now all I had to do was indicate the part and hit go.

By the time I finished I was averaging a little under 5 minutes each, so at $5 each with customer-supplied material and tools it slightly exceeded the $50/hr machine time goal I aim for. Setup and fixture/doohickey-making took about an hour and a half mostly because i just got a new lathe and I still don't have all the tooling for that set up well, so I had to do some workarounds.

The topic of this thread has got to be the most rediculous thread I have ever seen written. Way too much emphisis is placed on how much one can make in an hour. It appears to me with all your education, you still haven't learned anything about machining. You see, when your emphisis is on education, you read from a lot of books. You read books that somebody wrote who read a book that somebody wrote who read a book that somebody wrote, but how much time the the authors of any of those books actually spent out in the shop getting their hands dirty to prove what their scholarly associates wrote? Probably NONE!!

[FuriousGeorge]

The topic of this thread has got to be the most rediculous thread I have ever seen written. Way too much emphisis is placed on how much one can make in an hour. It appears to me with all your education, you still haven't learned anything about machining. You see, when your emphisis is on education, you read from a lot of books. You read books that somebody wrote who read a book that somebody wrote who read a book that somebody wrote, but how much time the the authors of any of those books actually spent out in the shop getting their hands dirty to prove what their scholarly associates wrote? Probably NONE!!

I found Sansbury's post interesting and informative; it's always nice to see how another machinist does things as there are usually a million "correct" ways to fixture and I often get set in my own ways. I found your post both pointless and unwarranted. Makes me wish this forum had a "dislike" option. Put your money where your mouth is and say how you would do it better. Don't criticize unless you actually have something constructive to contribute.

[JamesCordell]

good read i must say .. as in one post i was reading about how it has been suggested that it is difficult to judge under the impression of others work as what will productive and what will not be remain attached with the writers own perspective

[Just Me]

....I often get set in my own ways. I found your post both pointless and unwarranted. Makes me wish this forum had a "dislike" option. Put your money where your mouth is and say how you would do it better. Don't criticize unless you actually have something constructive to contribute.

I totally agree with you about Steve post...it is out of line and just an attack…
But Steve does make a fool out of himself all over the internet…He does not help Tormach reputation at all…

[sansbury]

The topic of this thread has got to be the most rediculous thread I have ever seen written. Way too much emphisis is placed on how much one can make in an hour.

Steve, you can be a real blowhard sometimes, but I'm going to take the high road and respond to this point because it raises an important subject.

I don't do machining full-time, and my primary focus is on my own R&D project, but I take on some additional work, partly for the money, and partly for the knowledge you gain in the process. I try to say "yes" to as many jobs as I have the time for, both because it leads to more work, and because it gives me more opportunities to learn. You may have a large network of customers who let you pick and choose only the perfect jobs in your sweet spot, but I don't, at least not yet.

When I bid a job, I try to estimate how much time it will take me, and how much the customer is willing to pay. I use $50/hr as a benchmark and try to not end up below it. If that nets out to $5/part and I think the customer is willing to pay more, maybe I'll start at $10. Rather than just lobbing spitballs, maybe you could share your wisdom with us on how you quote jobs. Because I don't know any other way.

And don't start talking about 'the race to the bottom' as if you're not part of it. You're competing against shops that are renting office space, paying all kinds of insurance, employee benefits, etc. Nothing wrong with that, this is just like computers going from mainframes to PCs on our desks. Sure some of the work you do is stuff other guys in your area don't know how, but if you weren't around to do it at a reasonable price I'm sure they could find somebody somewhere else. Try doubling your prices and see what happens to your backlog.

I've got another job I haven't talked about much yet because I'm waiting for the customer to publicly launch the product before I reveal anything about it. But it's also interesting because he found me and said he had a quote from a large shop to make his parts for $8 each. I figured that in order to make it worth his time to deal with a borderline amateur like me I'd do them for $4 (he provided the material, FYI). He said he needed 10 (10 each of 5 slightly different parts) and had no idea but might want more down the road. First batch I took a huge bath on because I was still learning the machine and my new CAM software. Three weeks later he was back asking for another ten and I spent a couple hours making the fixture I should have made the first time. That batch took less than half as long. Last week he came back for another set of ten and I think I'll hit my $50/hr target. Before it's done I bet I'll get five or six more batches out of him. If I'd passed on the first batch then I wouldn't have gotten the second or third. And I wouldn't have learned everything I've learned by figuring out how to make money on a low-profit job.