Precision Part Assembly Help

Machine Shop
#1

Im making machined spinning tops.

I am press fitting a piece of aluminium into a brass ring, and then a ceramic ball into that.
I also have a solid piece of brass with a whole sized to accept the ball I press as well.

Im using an harbor press for this operation at home and it seems when I press the ball in Im not pressing perfectly vertical and the ball shifts very slightly and is no longer centered. When this happens my top doesn’t spin well.
It creates vibration and imbalance and the tops visibly vibrate when they spin.

Does anyone have any advice on how to more precisely assemble these parts?
I have tried several ways and I cant consistently get everything aligned.

Any help would be greatly appreciated.

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#2

Off the top of my head, don’t press the ball into the top, press the top into the ball. I’ll explain.

Your tops for balance purposes are have tight tolerances on roundness and diameter. So is the center hole the ball is pressed into.

Create in hole in a block that is barely larger than the top diameter, .0005" - .0010" this will guide it down straightly. When making this hole put a small divot at the bottom that has the same curve as the diameter as ball but only 1/4th the diameter deep. This will provide full support with pinch points and center it precisely.

You can drop the ball in and it will center and rest in the divot on true center, when you insert top it will guide straight down and be aligned, then do the press fit. Pull top out and it’ll bring the entrapped ball with it.

Advantage is self centering and as the top comes in contact with ball it will ensuring it is centered in the hole at the bottom. Because the fit is tight no lateral movement of the top.

Simple tool to make.

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#3

I will give this a try as soon as I can, thank you. Ill let ya know how this work.
Its amazing that the tolerances are so small, I ruin so many of my tops pressing them.
Much appreciated.

#4

you’ve also got a flat arbor meeting a round ball which I’m sure they dont’ like each other. you need a concave arbor. you can get either of these ready made from the evil empire (tandy) or turn one yourself and set to the inner radius to match the bearing. I think that will help to keep them centered. cheers!

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#5

Buy a dapping block. Find the right size divot. Put your ball bearing in it and push.

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#6

I like this approach, but I’d be a little careful: if the tolerances on the jig are TOO tight, the even slight flaring at the end when the ball is pressed in might trap the top in the jig.

#7

The part where the ball is very small, sticks out from center and is at the center, you’d have to really hammer this down several times to distort the OD of the Top and the ball would be powder.

#8

Yeah, you’re right. I took another look at the photo. In my mind the ball was going into the shaft which went all the way through. This is not the case, and I am an idiot!

doh

#9

No, I had to go look at the original photo to make sure I didn’t make a mistake. It’s simple and everything can be aligned pretty accurately. Once he gets the pressure downright, it should go fast with just a light tap.

#10

I haven’t used the new lathe so I took the intro class last night, I cant wait to get in there and make the Jig

Do you think brass or aluminum would be better to use for the jig?

#11

I’d go with Aluminum much much cheaper and readily available.

You’re going to want to use inside micrometer or precision gauge pins, if we have them in that size. Calipers will be too imprecise for if you’re going for that precision. You can also just keep testing with top when you get real close. Make sure you have a sharp insert for the boring bar and slow fed slow wall finish is smooth and flood with coolant.

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#12

Thank you Sir, I ordered a 1.5" Diameter x 8" long piece from Plano Metal Supermart for 13 bucks, and its already ready for pickup.
If anyone is looking for metals they will sell any size any quantity.

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#13

You should be able to do this on the Sherline, but would recommend using the Clausing Colchester as it is more stable.

Mind if I ask a couple of questions?

  • What is the diameter of Top? How consistently can you hold this diameter to what accuracy.

The reason I’m asking, if you are investing in tooling to build many of these, lets say you can reasonably and consistently hold a diameter. You may want to buy a reamer to make the final hole size 0.001" over than diameter, with true excellent bore diameter and finish. Your tool will work better and should have reduced scrap.

Another option would be if you can drill a hole very precisely in terms of diameter and depth, so the ball just barely fits in, snugly optimally, them a tiny drop of expoxy at the bottom would hold it in place. Advantage to this is more flexibility in all the other dimensions as long as concentric and symmetrically about the center line.

#14

The diameter of the top is 0.995 inches. I think they are pretty consistent they are being made on a Cnc lathe. The hole for the bearing is made .0002 - .0004 smaller than the ball and the interference fit once pressed in holds it snuggly. I do have some that the bearing hole was exactly the same size and they might need some epoxy.

#15

A 1.0000" reamer will do what you want.