Author Topic: Pin Vices and Valve lapping  (Read 819 times)

Offline Brian Rupnow

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Pin Vices and Valve lapping
« on: March 07, 2019, 09:26:23 PM »
Many of you folks will know about pin vices, (also called finger chucks) but some are not aware they exist. This set of four cost me $30 including tax. They will hold round diameters from 3/64" (0.047") up to and including 3/16" (0.1875"). They are the perfect thing for lapping small valves into seats on model engines. As you can see, the part which you hold between your thumb and finger are knurled, and are small (-1/4") The chuck end on them is also relatively small, which means that you can grip the stem of an intake valve to lap it without having to remove the exhaust valve to get room to do it. (or vice-versa). When I make valves I turn them from cold rolled steel with a 92 degree included angle, and make the valve seats from brass with a 90 degree included angle. Then I insert the valve into it's guide and using first #300 grit and then 600 grit lapping paste I grip the stem of the valve in the appropriate pin vice, and while applying mild pressure of valve into seat I spin the pin vice back and forth between my thumb and finger. I generally put some #300 compound on the face of the valve, then spin it back and forth ten times, lift it up and turn it 90 degrees, and repeat another set of ten, until I reach a total count of 100. Then wipe off all of the compound and repeat with #600 grit compound. This will not give a wide contact area on the valve face where it fits against the seat, but it will give a very good air tight seal, which is all you need.-Be sure not to get any compound on the stem of the valve because you don't want the valve to be sloppy in it's guide.--And---never ever try and lap valves with a power tool. This must be done manually, with finger power only.

Offline b.lindsey

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Re: Pin Vices and Valve lapping
« Reply #1 on: March 07, 2019, 11:03:38 PM »
Great idea Brian, not to mention a good excuse to get some pin vise's  ;)

Bill

Offline Ian S C

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Re: Pin Vices and Valve lapping
« Reply #2 on: March 08, 2019, 02:17:07 AM »
for valve grinding you could make something similar from a scrap of steel from the junk pile, I have a couple that I use as handles for 1/8" needle files, they also work as tap wrenches for 1/8" / 3 mm taps. Can be made to what ever size you need.
Ian S C

Offline Brian Rupnow

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Re: Pin Vices and Valve lapping
« Reply #3 on: March 08, 2019, 07:42:27 PM »
Ian--You might be able to make something like it from your junk pile. I guess to a large extent it depends on what you value your time at. An hour of my time buys 1 1/2 sets of these things. I doubt that I could make one alone in less than three hours.

Offline simplyloco

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Re: Pin Vices and Valve lapping
« Reply #4 on: March 08, 2019, 09:42:25 PM »
I use mine for tapping 1.2mm metric threads, by hand!
John

Offline Ian S C

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Re: Pin Vices and Valve lapping
« Reply #5 on: March 09, 2019, 12:43:55 PM »
True Brian, but when I made mine it was/is 40k to get to town(I don't drive), and when I got there nothing suitable, so home again. My time's my own. I suppose I could have got on the phone and had a ring around, and got it sent out, but I like to see things before I buy, a bit old fashoned.
Ian S C