How to press fit a pin into a hole ?

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compact8

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I am looking to make a sine bar and the design I use requires a pin to be press-fitted onto a steel plate. The pin will not be subject to any stress but it need to stay in place securely. Assuming that I can drill a hole of diameter exactly the same as that of the pin, will it be possible to press the pin into the hole with a bench vice ? I believe the key is to ensure that the pin is perfectly perpendicular to the plate in the process and I cannot figure out a simple way to do it. Will appreciate some hints.
 
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"Assuming that I can drill a hole of diameter exactly the same as that of the pin". That is a mouth full. If you are looking to press fit a pin you should be looking for a very round hole that is slightly undersize of your pin. .0002 to .0005 is where I would want to be. The industry offers pins that are + or - .0002 of the standard pin size. I hope you are planning on reaming the hole to size. It would be very difficult to drill a hole with a drill bit round enough to friction fit a pin. Having said that, if you can drill a hole that is a couple tenths undersize, yes you could press the pin in any number of ways. A vise would work. For the most part, the pin will follow the hole, so you might try starting the pin by tapping it gentle with a brass hammer.

To give myself a little advantage sometimes, I will put the pin in the freezer for an hour or so and insert it while it is still at its peak of cold.
 
It's much easier to turn a pin to fit an existing hole than vice-versa
If the pin is too large or the hole is too small you will never get it in- it may go only part way and stop- at which point you break your vise
trying to force it all the way
Chamfering the pin and the hole edge will help get it started
Freezing the pin and heating the hole might help too, but you have to work fast
 
The ends of pre-made dowel pins typically are chamfered or rounded, making it easier to get them started into a hole. At least the ones I've purchased have been.

I've used my vise to seat them, once the hole(s) were reamed to size. I own two sets of reamers. One is a collection of over/under reamers from 1/8" to 1/2", and the other is an on-size set. That way I can get anything from a press fit to a sliding fit, depending on what the application is. In one case I used two different sizes to make a low-profile vise (it installs on the side of a home-made sine table). The movable jaw has two press-fit dowel pins and the edge of the sine table has two matching holes reamed for a sliding fit. That way the jaw doesn't lift when I tighten the jaw with screws.

Once I tried driving in a dowel pin with a hammer. That didn't work out too well.
 
homebrewed said:
. I own two sets of reamers. One is a collection of over/under reamers from 1/8" to 1/2", and the other is an on-size set.
Click to expand...
This Over/under reamer set is something I use way more than I thought I would. It makes pinning parts together so easy that I consider that first instead of bolting or screwing.
 
Use a small vee block to keep the pin perpendicular to the workpiece . If I'm making anything to be pressed , I always machine a lead .001 under the hole size on the pin . Makes for easy alignment .
 
Answering your vise question directly, Yes, you could press a pin in using a bench vise.

As mentioned above, drilling doesn't leave an accurate hole. The best way is to drill a slightly undersized hole and ream it to size. Judging from your location, you are likely using metric sizes. I have an over/under reamer set in common English sizes that are +/- 0.001" from the size (0.249" / 0.251" for a 0.250" hole). I would imagine there are over/under reamers (you'll need an under reamer) for metric sizes also.

Bruce
 
Have two comments, both from experience.

Please don't use your vise. It may work if everything is perfectly sized, or your vise will break, like mine did. You need an arbor press, or something like it.

Second, having an over and under reamer set is great. Before you use it however, please check that the reamers are what they are supposed to be. I had to return a whole over-under reamer set because the undersized reamers were all nominal size! Every single undersized reamer was oversized. Reamers are easy to check for size with a micrometer.
 
This is a funny thing that came up at work the other night . One of our mechanics pressed a .375 diameter sleeve into one of our dies . This was suppose to be a slip fit . They crunched the sleeve to the point it was .030 oversize and they couldn't figure out why it didn't fit into the other die half . I had to take a boring head and machine the 30 thou off the OD in the mill . I sent a pic to @Aukai that night , maybe he'll post it if he sees this post . :grin:
 
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