Peter Neill
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I've aready posted this over at HSM, so apologies to those who are now having to view it twice.
Not a lot to do with Models (well nothing actually if I'm honest.. ;D), but it was an interesting little project so I though I'd post it.
Heres a little project I did today.
As some of you might know, I run a small Injection Moulding business, and we make the part shown in the first picture below. Its heavily glass-fibre filled carrier that holds stainless steel US transducers, and there was a problem with the fit of these. They have to slide in the pockets with a spring loaded close-running fit, but not tight, and they were binding on the little crush rib bumps that run vertically down the pocket.
Another problem was that the assemblies with these were part built with another component wired up and fitted on top, that couldnt be disassembled, so I had to come up with an plan to ease the fit and make it all slide again.
Hand filing or knife trimming was out, as this wouldnt produce the exact size need for the sliding fit, so I had an idea to make some little hand punches to do the job.
The next four pictures show how I made them.
I needed 3 punches, so the first step was turning up 3 blanks from O1 tool steel.
The next step held the blanks in a 5C collet block on the mill, and the rectangular pocket form was cut, leaving plus 0.005/side for a grinding allowance.
A centre relief pocket was then milled out to provide clearance for the transducer mounting connectors in the pre-assembled parts.
The punches were then hardened, and surface ground back to the exact size on all 4 faces, and a chamfer ground on all corners, again using the surface grinder. The grinding setup used the 5C collet block to register all the faces.
The final picture in the first set shows the already ground blocks set up again to grind a 5 degree back angle to produce the cutting edge.
The plan was to mount these in some handles with a spring loaded depth-stop, so that they could be pushed through to depth without contacting the assembled parts, so making these was the next step.
I had some 25 mm Acetal bar, so this was cut to length, drilled to take the shank of the punch, and counterbored to make a spring seat.
Next step was over to the mill to put in a hole for the M4 Cap Screw that would hold the punch. Because these were going into round bar, I wanted a smaller c/bore than normal, so used a 7mm drill instead of a proper c/bore cutter. A little trick to get the right depth is to hold the head of the Cap Screw against the fixed depth stop, and wind up the threaded stop to pinch it, and correct depth is set.
The unhardened shank was drilled and tapped to take the M4 screw.
In the meantime I turned up some stop collars and ground these back to to a uniform height, and the punches were then assembled to the handles.
he final step was testing it out to make sure it all worked.
The finished hand punches are shown in the first picture.
The second picture shows the finish ground punch, and you can just make out the 5 degree back angle on the edge. I didnt want a sharp knife edge on these, as that would have too much potential to dig-in to the plastic, so I decided that a 1mm edge with a back-angle would do the trick.
The third picture shows it in place in the transducer pocket and up against the stop, and the final picture shows it as its about to punch through and trim the pocket to size.
Measuring before and after showed that it shaves off just over 0.0015 from the crush ribs, and this is just enough to get a nice sliding fit on the transducers.
Peter
Not a lot to do with Models (well nothing actually if I'm honest.. ;D), but it was an interesting little project so I though I'd post it.
Heres a little project I did today.
As some of you might know, I run a small Injection Moulding business, and we make the part shown in the first picture below. Its heavily glass-fibre filled carrier that holds stainless steel US transducers, and there was a problem with the fit of these. They have to slide in the pockets with a spring loaded close-running fit, but not tight, and they were binding on the little crush rib bumps that run vertically down the pocket.
Another problem was that the assemblies with these were part built with another component wired up and fitted on top, that couldnt be disassembled, so I had to come up with an plan to ease the fit and make it all slide again.
Hand filing or knife trimming was out, as this wouldnt produce the exact size need for the sliding fit, so I had an idea to make some little hand punches to do the job.
The next four pictures show how I made them.
I needed 3 punches, so the first step was turning up 3 blanks from O1 tool steel.
The next step held the blanks in a 5C collet block on the mill, and the rectangular pocket form was cut, leaving plus 0.005/side for a grinding allowance.
A centre relief pocket was then milled out to provide clearance for the transducer mounting connectors in the pre-assembled parts.
The punches were then hardened, and surface ground back to the exact size on all 4 faces, and a chamfer ground on all corners, again using the surface grinder. The grinding setup used the 5C collet block to register all the faces.
The final picture in the first set shows the already ground blocks set up again to grind a 5 degree back angle to produce the cutting edge.
The plan was to mount these in some handles with a spring loaded depth-stop, so that they could be pushed through to depth without contacting the assembled parts, so making these was the next step.
I had some 25 mm Acetal bar, so this was cut to length, drilled to take the shank of the punch, and counterbored to make a spring seat.
Next step was over to the mill to put in a hole for the M4 Cap Screw that would hold the punch. Because these were going into round bar, I wanted a smaller c/bore than normal, so used a 7mm drill instead of a proper c/bore cutter. A little trick to get the right depth is to hold the head of the Cap Screw against the fixed depth stop, and wind up the threaded stop to pinch it, and correct depth is set.
The unhardened shank was drilled and tapped to take the M4 screw.
In the meantime I turned up some stop collars and ground these back to to a uniform height, and the punches were then assembled to the handles.
he final step was testing it out to make sure it all worked.
The finished hand punches are shown in the first picture.
The second picture shows the finish ground punch, and you can just make out the 5 degree back angle on the edge. I didnt want a sharp knife edge on these, as that would have too much potential to dig-in to the plastic, so I decided that a 1mm edge with a back-angle would do the trick.
The third picture shows it in place in the transducer pocket and up against the stop, and the final picture shows it as its about to punch through and trim the pocket to size.
Measuring before and after showed that it shaves off just over 0.0015 from the crush ribs, and this is just enough to get a nice sliding fit on the transducers.
Peter
