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BLACK BELT
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7,084 Posts
Discussion Starter · #1 ·
I have a roller bearing [HN 1816] with an O.D. of 24.00 mm.

What size should the hole be for pressing the bearing into?

The material is titanium, if it matters.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #2 ·
Would this be correct for the bearing?

-0.00075" to -0.0015" interference fit = must be fit using hydraulic press (or other press)


I also have a titanium rod (bushing) that fits into a titanium hole, and I want a precise slip fit.

Does this sound right?

0.0010" to 0.0000" slip fit = still seemingly tight by hand, but will slip fit without perceivable slop
 

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Premium Member
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yeah... about one thou per inch..

ive always made bushings as bang on as possible for the od.. but you'll need some space on the inside or w/e that you're bushing.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #4 ·
I think I'm gonna go with half a thousandth over for a slip fit and half a thousandth under for a press fit.

I can't understand how people can machine to these tolerances, anyway.
 

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lɐʇuǝɯᴉɹǝdx&#4
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3,517 Posts
One of my bearing pockets was about .005 over, still was a loose slip fit (I added green locktite). The other was maybe .002 over, needed to press in with a bit of force and use a drift & hammer to get it out, but was a true slip fit. Material was 7075-T6 aluminum, MoE of ~10000 ksi. Titanium alloys run closer to 16000 ksi, but that's only relevant if you go for an interference fit. Bearing was a bit bigger than yours (1 5/8", iirc).

My guess is if you can hold within .0005" over, you'll still need a bearing press. And yeah, those tolerances are hard, and you have to trust your bearing to be in the same tolerance, or measure it with something really precise. In my case, measuring was probably the bigger challenge than holding tolerance; we didn't know exactly what to cut to until we got there.
 

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Is my bike ok?
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don't forget to measure at room temp .
Or, at least have all of the pieces in the same room for an appropriate amount of time for all of the temps to normalize with each other. My shop is usually in the 50's during the winter, and in the 80's during the summer. Which one is room temp? :D
 

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BLACK BELT
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Discussion Starter · #8 ·
Okay, I guess it's not going to be that easy - and I may not be able to get it right. If I make a mistake, it will be VERY costly.

I'm starting to understand the dynamics of the slip fit and the press fit.

A hole in titanium needs to be larger than a hole in aluminum because of the hardness of the metal.

The size of the bearing also makes a difference - the larger the bearing, the more resistance to pressing.

The hole size needs to be very precise in order to remove and replace the bearing, which I need to do.

Pretty sure "a half a thousandth over/under" isn't going to be right.

Even if I figure it out, I'm not sure who can do this kind of machine work.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #9 ·
One of my bearing pockets was about .005 over, still was a loose slip fit (I added green locktite). The other was maybe .002 over, needed to press in with a bit of force and use a drift & hammer to get it out, but was a true slip fit. Material was 7075-T6 aluminum, MoE of ~10000 ksi. Titanium alloys run closer to 16000 ksi, but that's only relevant if you go for an interference fit. Bearing was a bit bigger than yours (1 5/8", iirc).

My guess is if you can hold within .0005" over, you'll still need a bearing press. And yeah, those tolerances are hard, and you have to trust your bearing to be in the same tolerance, or measure it with something really precise. In my case, measuring was probably the bigger challenge than holding tolerance; we didn't know exactly what to cut to until we got there.
I need a slip fit for a 20mm bushing and an interference fit for a HN 1816 (24mm) bearing - both into titanium.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #10 ·
Getting closer. Been searching and reading a lot. Got new info and ideas.

One idea is to fit a bearing into a test piece to determine the hole size before machining the relay arms.

I also found an interesting number from one of the bearing tables: 23.976mm. Not sure, but I think this is for steel. It does fall between .0005 and .001 inches smaller than the bearing OD. Might have to go on the smaller side for titanium.

24.0000mm = .9448in
23.9872mm = .9443in = .0005in smaller
23.9760mm = .9439in = .0009in smaller
23.9745mm = .9438in = .0010in smaller

Need to get CAD done and look into machine shops and cost estimates.
 

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Is my bike ok?
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A thousandth of an inch is actually pretty damn big once get used to hanging around machines for just a short while. I'm sure Sebspeed or DB could handle did kind of accuracy with ease.

Who's been doing all the machine work in your builds? They can't bore this hole for you?

Also, what are you working on.? Why do you need a CAD drawing to bore one hole?
 

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lb/hp is what it's about!
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My experience machining titanium is limited and the few times I worked with it never required a press fit but I'd say a .0003"-.0007" press fit would be good.

Shinyribs is right though. As long as the machine is decent and the machinist knows what they're doing holding a tolerance in the tenths isn't hard to do. The one shop I was at made a lot intricate microscope parts and a bunch of stuff for the aerospace industry and we had to hold tolerances like +.001"/-.000" pretty often.




Obviously tighter tolerance parts take longer to make or a scrap part can be expected before making a good one. Here is a chart to show that holding a tolerance in the tenths isn't cheap.

 

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HipsterKillerGarage
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6,484 Posts
Bore size .9439".

Class IV fit. Capable hand press. No wobble or bearing movement. Perimeter of race fully supported. Capable of removal for replacement.
 

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HipsterKillerGarage
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6,484 Posts
.9430" - .9446" is the range you are looking for BTW. Max material condition @ .9430", min @ .9446".

The number in the post above is midway.

For a little easier fit, go towards min. mat. cond. on the bore.

Note- max mat above will likely require you to use tools to get the bearing in. Like, the bearing isn't gonna fall out or easily work it's way out at that point.

What's the application and rpm's/position of this assembly?
 

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HipsterKillerGarage
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6,484 Posts
There's one other consideration.

Tell the machinist you want a class 4 (hand press with tools) or class 5 (hydro/arbor press) fit. If he doesn't know what those are you shouldn't let him machine shit anyhow. Hahahaha
 

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Is my bike ok?
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15,025 Posts
Bore size .9439".

Class IV fit. Capable hand press. No wobble or bearing movement. Perimeter of race fully supported. Capable of removal for replacement.
Does hand press mean pressing in using only your bare hand, or using a light arbor press?

Bearings for relay arms will need more resistance than pushing them in by bare hand, IMO. A fit that loose will allow the outer race to turn too easily.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #17 ·
Does hand press mean pressing in using only your bare hand, or using a light arbor press?

Bearings for relay arms will need more resistance than pushing them in by bare hand, IMO. A fit that loose will allow the outer race to turn too easily.
Hand press as opposed to a hydraulic press. Hand press is the correct application.

Most of the hand press tools I've seen are just threaded rods with nuts and adapters.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #18 ·
Who's been doing all the machine work in your builds? They can't bore this hole for you?

Also, what are you working on.? Why do you need a CAD drawing to bore one hole?
The block of titanium has been sitting at the local machine shop for months. The machinist could do it, but he's very lazy and only gets the simple stuff done. Their machines are old, and can't use any modern CAD programs, so he has to draw everything himself using an old program. There was a great machinist there, but Disney stole him away $$$$$$$$$$$.


I'm trying to make modified titanium relay arms to replace the steel OEM arms. I know a roller bearing would not be recommended, but I think it will be okay. (There is also a backup plan using steel inner bushings, instead of titanium, and bronze outer bushings.)

 

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BLACK BELT
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7,084 Posts
Discussion Starter · #19 ·
A thousandth of an inch is actually pretty damn big once get used to hanging around machines for just a short while. I'm sure Sebspeed or DB could handle did kind of accuracy with ease.
I hope so! Not sure who's willing to work with titanium.

I should have shown the relay arms in the first post.

My version of the relay arms uses a simplified (shape) design and no grease fittings.
 

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BLACK BELT
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7,084 Posts
Discussion Starter · #20 ·
Bore size .9439".

Class IV fit. Capable hand press. No wobble or bearing movement. Perimeter of race fully supported. Capable of removal for replacement.
Thanks for posting!

Your numbers are pretty much the same standardized numbers I posted on the bottom of page 1. The issue is- I'm not sure where in the range will be correct for titanium.

Not sure if you're familiar with Young's Modulus, but the answer may be there. :D

Aluminum: 69GPa
Titanium alloys: 105–120
Steel: 200GPa
 
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