What's new
What's new

Best way to make keyed hole(D shape)

Andy_paul

Cast Iron
Joined
Aug 30, 2005
Location
Texas
I'm sure everyone has seen the D shaped hole that stops rotation on many types of panel mount or bulkhead mount electrical connectors, potentiometers, fuse holders etc with the threaded jam nut. What is a good way to make this hole on a manual mill? The holes I will be doing are .375 to .5 in ABS plastic that machines really nice. I know I could do it with a rotary table, but there has to be a faster way.

Would a hot punch work to just melt the shape in? This would work on the plastic ones, but I may have to do some in aluminum as well.
 
Greenlee chassis punches are insanely expensive. I have a set for most of the holes I need to make. (D, double-D, serial, SCSI) Greenlees run about $400-$500 per punch. It is also quite slow unless you are doing one offs and prototypes. Another option is a CNC mill or CNC router with a small diameter bit. Most places I know that do limited production runs farm them out to a specialist.

On major production runs of plastic panels the holes are molded in.

You could also make your own broaches.

One other option (if you can find them) is special washers that go under the bezel ring. The washers have the right shaped hole and a little tab that goes into a small hole drilled near the main one to stop the washer from rotating. I often use those for toggle switches. They have a little "tooth" that engages the slot in the toggle switch shaft. They are also available in D and double-D shapes.

-DU-
 
if you make a D shaped insert that drops into the parent material you're not making the D shape in a blind hole - might making broaching a possible.

overkill for plastic ..... but I've made these before via a built up assembly in brass. drill/ream and turn od of 'insert'. mill out a section and solder a flat piece there. back to the lathe to re-turn the OD & part off. now you have a round OD and D shape interior ready to loctite into a bore. the pic is from my old digital camera and is crap, but you can make out the outline of the insert and get the idea

dcloseup.jpg
 
David said, "It is also quite slow unless you are doing one offs and prototypes." So true. I now use an electric impact wernch on them, really speeds them up but lube on the threads is a must.

Bob
 
I think the punch is out of the question for sure as the bezel is very small, plus the price. Out of curiosity, how does one index the punch to make the hole location accurate within a few thousandths? I have never used one before.

Mcgyver, that is very interesting, I would have never thought of that, D hole stock so to speak!

Thanks!
 
You are never going to punch that in 0.375 or 0.5" plastic. Not practical.

I'd think you could make a nice broach to do that starting with a smaller round hole. Wouldn't take much for those plastics.

Milling is too much like work, and you can't get the sharp inside corner.
 
We drill 1/8 holes near as we dare to the 2 corners then drill the largest hole we can, than broach them with a broach made of drill rod and do thousands of parts with a vmc up to 1/2 thick aluminum.
 
Rotary Broaching the D

Plan D: Rotary Broach tools are available in D shape, but the maximum recommended 'tooth height' for this type of tool in steel is about .010. The one continuous chip on a rotary broaching application creates alot of pressure. With a rotary broaching tool, you would pre-drill to the largest possible diameter, then broach the remaining 'fingernail' or 'moon' shaped chip. You could only rotary broach a shallow depth though, because of the extreme chip accumulation.
 
d hole

if the abs is .5 thick, drill a round hole, glue in a spline or cross piece. or if you want to get fancy, start with a piece of round stock and slice off the section and glue that it. Universal pipe cement works very well on abs.
if the abs is .05 thick, you can get an arch punch, these used to be standard, I had a large set that I kick myself for not saving. If not standard, a die maker that makes forged cutting dies for leather, can make one, maybe 100 bucks.
 
Yes, Greenlee prices are high.

I have a collection of close to three dozen Greenlee punches. Well, one or two are other brands. Included are all the round sizes from 9/16" to over 2" diameter as well as many other shapes like squares, rectangular, and D and Double D punches. And I got them almost free. HOW?

First, the common, round punches are a lot less expensive than the more complicated shapes; less than $100 vs. $200 and more.

The chassis punches (often mislabeled as knockout punches) are often sold on E-Bay in lots of multiple punches in various sizes. And these lots often go for the price of a single punch or even less. I bid on and purchased a bunch of these lots.

Often these used punches were badly worn. But chassis punches (including the very few sizes that actually are knockout punches) are dead simple to sharpen. The female part is simply held against the flat of a wheel. And the male part on most of them will have two angled facets that are also just held against the flat of a wheel. That's it. A minute or two and it is factory sharp. It is a lot easier than sharpening a drill bit. You almost can't go wrong.

So I said my collection was almost free. How? Well, in purchasing multiple assortments I wound up with multiples of a single size. So I sharpened them, replaced any missing draw bolts with grade 8 bolts, and sold them INDIVIDUALLY on E-Bay. I described the improvements I made so the buyer would know he was getting a usable tool. I offered a no questions return policy. And the repaired and sharpened punches sold for much higher prices than the dull ones in the collections that I purchased. I am sure I acquired the collection of dozens of punches for less than $75 total.

PS: you don't even need a grinder to sharpen them. It can be done on a sheet of sandpaper laying on a flat surface.



Greenlee chassis punches are insanely expensive. I have a set for most of the holes I need to make. (D, double-D, serial, SCSI) Greenlees run about $400-$500 per punch. It is also quite slow unless you are doing one offs and prototypes. Another option is a CNC mill or CNC router with a small diameter bit. Most places I know that do limited production runs farm them out to a specialist.

On major production runs of plastic panels the holes are molded in.

You could also make your own broaches.

One other option (if you can find them) is special washers that go under the bezel ring. The washers have the right shaped hole and a little tab that goes into a small hole drilled near the main one to stop the washer from rotating. I often use those for toggle switches. They have a little "tooth" that engages the slot in the toggle switch shaft. They are also available in D and double-D shapes.

-DU-
 
As for mounting electrical and electronic controls and devices in holes in 3/8" or 1/2" plastic, THAT IS INSANE.

I have made many, many custom electronic control panels and can tell you that almost NO electric or electronic controls or other devices are made to mount in a panel that is that thick. Generally speaking, from a lot of experience, the range of panel thickness that the parts are made to mount in is 1/16" or LESS. The thickest panels that I have made were 3/16" but I often had to either mill that thickness down on the rear or use thinner plates fastened over a larger hole to mount many parts. Even then, adding one or more stiffeners on the back of a thinner panel is better than using a thicker one.

The general way that electric and electronic enclosures are made is with a front panel that is 1/8" thick or THINNER. In my opinion, after decades of practical experience, 0.050" aluminum is the maximum thickness that is practical for such construction. Only when the panel is very large would I consider using thicker material. And chassis punches are the ideal way to create the odd shaped holes.

But many electric and electronic components have a built in bezel on the outside of their mounting section. This bezel can cover parts of the openings that are not strictly necessary. So a small milling cutter, like 1/8", can be used to make openings for a variety of parts that have odd shaped openings. Here's some examples:

attachment.php

Double D Fuse Holder

attachment.php

D Shaped Hole

attachment.php

Rectangular Hole

attachment.php

D Sub-miniature Connector

In the case of the D Sub-miniature connector, the second, alternative cutout is something that I have seen on some expensive, high end, professional equipment. A punch of that shape was used by a major manufacturer as an alternative to a more expensive one with the "proper" shape and the three holes. I have one of those proper, three hole punches and new, it cost over $200. Of course, I got it for a song on E-bay.

As far as I know, no one makes either punches or other tooling for cutting these odd holes in 3/8" or 1/2" panels, even if those panels are plastic. Milling would be the only way and you would have to mill a well on the rear for the actual body of the part to fit in while it is supported by only the front 1/16" or less of that plastic. That is going to be a more expensive way to do it.
 
One more thought on this. One good way to make a professional looking panel for a plastic box is to use an aluminum panel that has been etched with the needed markings for the components. That, relatively thin panel is then drilled, punched, and milled with the needed holes. This produces a very professional looking, custom front panel that is extremely durable. And it can be done in small quantities.

If you need larger quantities then you can have the aluminum panels made for you by shops that specialize in that. A web search will find them.

EDIT:

OH FOR PETE'S SAKE, IT'S A 12 YEAR OLD THREAD. WHY DO I KEEP GETTING CAUGHT BY THEM?

THESE OLD THREADS NEED FLASHING LIGHTS OR SOMETHING.
 








 
Back
Top