Making parts in batches. Fixures, jigs and stops Oh MY!

[gadget_lover]

In another thread, LLcoolbeans wrote;

I would love to make accessories for the vastly popular NC and Fenix lights. There is one problem, however. These lights generally retail for around $50. Anything I do is all hand done with manual machines, so the problem is price. Someone willing to pay upwards of $150 for a light might be willing to pay $50 for a custom bezel. But would someone be willing to pay $50 for a custom bezel for a $50 light. Therein lies the problem.

Unless I can contract out and have them mass produced, which is certainly worth looking into, price will never be viable.

The point is a good one. How does one make a large number of parts with a reasonable amount of time and effort?

The CNC milling center is a relatively new tool for most machine shops. 30 years ago they were only available to big shops and factories. They are becoming quite common, but are still outside the budgets of most home shops.

So how did Henry Ford manage to build 18000 cars the first year? How did Mattel build and sell 350000 barbies the first year? The answer to both is the concept of fixtures, jigs, molds and stops used in an assembly line.

When you are making a part the biggest time consumer is setting up the part to make the cuts. You have to clamp the part in something an then accurately measure and then set up the right tooling and then do the actual cuts. A lot of those steps go into a small CNC machine too.

So to make a bezel you will bore, turn, thread, possibly add grooves for o-rings and knurling or other decoration.

But if you are doing 50 bezels, you might do it differently. By doing the same thing to 10 or more pieces at a time you save the measuring and tool changes and adjustments. By using a collet with a depth stop in it you can mount each piece in exactly the same way in a fraction of the normal time. By using carriage stops you bore to the same depth on each one without overshooting.

If doing 100 bezels it might be worthwhile to buy or make a tap instead of single pointing it. Taps are just as accurate if done right.

The real machinists can give you much better tips than this.

Daniel

 

[precisionworks]

I sometimes do a contract run of a few hundred parts, fairly tight (+/- .0010" on the OD, +/- .0005" on the ID, typical). Since all my tools are manual, the sample parts & .dwg files are taken to a nearby CNC shop. If no samples are available, just the .dwg files are emailed. He has a quote back within half a day if he's in the shop.
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I take his actual charge, plus the cost of the material I supplied, add my handling fee, and come up with a total cost for my customer. You normally don't make a ton of money that way, usually a few hundred dollars at most, but it adds up over the course of a year. It has always averaged more than my shop rate of $60/hour.

Downside is you have zero control of the finished product. That isn't an issue as long as you carefully choose the CNC shop. I work with two, one within 5 miles, the other 25 miles, and both are killer shops. One does some defense work for General Dynamics, and was a field tech for Mazak before that. No surprise that his HMC's and VMC's are all new or slightly used Mazak's

fixtures, jigs, molds and stops used in an assembly line.

For smaller runs, or where the price goes too high if a CNC shop is used, that's the way to work. On one simple job, here's the work flow:

Have 1/2" x 2" x 20' sticks of flat steel delivered. Cut them into 2" long sections, using length stop on bandsaw

Drill each 2" x 2" square for tapping with 1/2NC tap

Tap all squares

Deburr & chamfer holes

A dedicated, camlock vise (with stop) makes sure the hole goes in the right place. A tapping head eliminates start/stop/reverse/stop for each part. The Burr King does a fast job of deburring.

Boring as hell, but it pays the bills, shows a profit to the business account, keeps all the tools & tooling tax deductible, and makes SWMBO happy

 

[rescue15]

There is a plastic specialty shop near me that uses a CNC to turn out custom products. I have used them twice once to make stepped lenses for a mag light mod adn again to make a lid for a custom diving canister light. Both times the price was not out of the reach of a hobbist. If yo look hard enough I bet there is a similar shop near you.

Steve

 

[gadget_lover]

The other day I needed to transfer a bolt pattern to a new bracket. The bolt pattern was two sets of triangles in about a 1 inch apart. They were tapped for 3 mm screws. I did not want to disassemble the part in order to transfer the pattern using punches.

To accomplish this I mapped the locations of the holes using the memory of the DRO. I used a wiggler in the quill of my mill to accurately locate the holes.

The DRO will store 200 XYZ locations. I simply put the part in my mill (with an stop so I could find the place a second time) and used a ball ended wiggler to locate each of the holes. When I had it indicated in I saved the location in one of the the DRO memory slots as X=0, Y=0.

After that, I could make as many brackets as needed by mounting the bracket against the stop in the vice and then recalling the location for each hole. Once I moved the table to 0.0000, 0.0000 I could then drill, countersink, enlarge, etc.

I found that after test fitting the bracket I could put the part back in the vise and do repeat operations too.

The fit was accurate enough that the bracket moved freely in and out with 1 inch screws in all the holes. The clearance on the holes was deliberately tight.

Daniel
P.S. I posted this in another thread, but thought it should be here.

 

[LEDobsession]

If you guys are interested, my neighbor is a long time master machinist and he made and patented a design for an amazing part stop that he sells for about 30 bucks I believe. Check out his YouTube video if you're curious. I can honestly say its the best part stop I have.