Fitting Alignment Pins - Oversize Holes

[CNC Molds N Stuff]

A while back we had a discussion on here somewhere about putting alignment pins in slightly larger than average holes.  I was a big proponent of knurled pins.  I've knurled lots of stuff in the past.  Tool handles, injector nozzles, lock and adjuster nuts on optical mounts, and on my home made carbide scribes.  

Well, I accidentally drilled some press fit pin holes with the clearance size drill bit the other day.  Oops.  I decided to prove my point.  Unfortunately the stainless that my stock pins is made of would not take a big enough knurl to do the job.  I studied it on it a bit, and then decided to do some experiments.  If the hole was only a thou or two I could get enough, but at 4 thousandths over size it was tough.  Now I could have delved into my sealants and adhesives cabinet and dug out some of the exotic Loctites I have in there, but I wanted to see what the mechanical answers were.  You can shim a hole of course, but its hard to do so it looks good.  Maybe for my own mold, but not for a customer.  

Finally I just did it the easy way.  I turned custom pins.  No kidding.  I keep 416L and 303 stainless rod (in a pinch my local metal vendors stocks 304) on hand for various other projects in a few sizes, so I just picked up a piece of 416 that was larger and  turned it two about 3 thousands larger than the over sized hole.  Then I turned the part that would stick out of the hole to the standard size to fit the clearance hole on the other plate, and radiused the end the way I normally do.  Works perfectly.  Now I wouldn't want to have to do hundreds of them, but the 5-10 minutes it took me to do one set was certainly more efficient than recutting the mold from scratch.  Now that I've done a set could probably do it 2-3 minutes in the future.  especially if I move the small lathe into the machine room with the big lathe so I don't have to walk back and forth.  

Making custom pins was the fastest  and easiest way to do it.

Now I want to be clear.  I have knurled a pin to over size it to have an interference fit in a hole many times, but I've never done it before with such a small pin with that alloy.  My vendor just says 18-8 which encompasses a whole range of stainless alloys.  

I hesitated to post this for a few days, because I know some guys who never make a mistake at anything might take it as an opportunity to be negative, but then I thought.  So what.  By posting this I might help somebody.  

Edited April 13, 2017 by CNC Molds N Stuff

[CNC Molds N Stuff]

A lathe should in my opinion be part of any semi-serious home shop "maker's" work shop.  Even a small POS mini lathe is better than no lathe.  Lots of places sell them.  My first lathe was a Harbor Freight 7x10 my wife bought for me for Christmas one year.  I used it to make a shoulder bolt and repair a knife my son gave me as soon as I got a few cutting tools for it.  Now You can't buy anything but mini lathes from HF anymore.  They aren't great, but if you don't break them from pushing to hard they will get you by.  I'd probably goto Grizzly or Little Machine Shop instead of Harbor Freight if I bought one today, but I did a lot of work on that baby lathe.  I still have it, but it doesn't get any use these days.  I am halfway thru a CNC conversion on it.   I've got a slightly larger Harbor Freight lathe that gets used everyday during the week to radius alignment pins.  A collet closer makes it very fast for repeat work on parts the same size... like putting a radius on alignment pins.  For more serious "projects" I picked up a Precision Mathews PM1440 LBE that puts both of the smaller HG lathes to shame.  I use a big 3 jaw most of the time.  Its great for turning down stock to make a part in a  single setup, but when I need precision or to work on an existing part I swap out to a 4 jaw.  I was skeptical about the 4 jaw the first time I used it, but then I watched a couple videos on dialing in a part with an indicator and now it only takes a minute or two.  Sometimes I get lucky and it only takes a couple quick adjustments.  I expect with more experience I'll get lucky more often.  I originally thought I'd use it to make injectors, but I just haven't had the time.  Mostly it gets used for one off projects. 

My advice is if you are a maker or tinker is buy a lathe.  The biggest & best one you can afford and fit in your space.  Bare this in mind though.  I can easily turn a tiny 1/4 inch pin on the one (1) ton 1440, but I can't slide a piece of 2 inch rod through the bore of the little 7x10 and I certainly can't pop out the gap to turn a part that's 20 inches in diameter.   If you can afford it and if it will fit in your shop...  Its better to have it and not need it than to need it and not have it. 

"But I don't do any metal work Bob.  I don't need a lathe."  Maybe, but a wood lathe sure might be handy.  Making poppers and wood choppers for tackle makers.  Replicating a broken chair leg for others.  I've got one of those too, but I admit I don't use it much.  Often basic turned parts like furniture feet are cheaper to buy than to make, you know in the back of your head that somewhere somebody has a piece using those same feet... and it makes it look like yours. 

Lathes are one of the oldest machine tools.  They date back to about 1300BC.  https://en.wikipedia.org/wiki/Lathe .  They are credited with being the first tool capable of being used to recreate itself.  Maybe not so much with modern bearing assemblies, but they can certainly make a precision bushing capable of being used to make another lathe.  The first thing I ever recall personally seeing a lathe used for in fact was a replacement bushing for a washing machine motor.  When I was a kid my grandfather had me watch while he made it. 

At the very least make a big batch of cookies for a neighbor who owns one. 

Edited April 16, 2017 by CNC Molds N Stuff

[mark poulson]

" They are credited with being the first tool capable of being used to recreate itself. "  My dad was a lathe hand, and told me that years ago.