Press Fit
 

I had a few questions about press fitting, Specifically bearing's. Lets say I want to press fit a bearing into and 1/8" plate, the bearing's OD is 5/8. Do I drill a 5/8" hole? Because we tried that this year and we needed epoxy to keep it in place. Next question, Can you press fit into 0.09" sheet? or is that to slim? Any information is very appreciated!

Re: Press Fit
 

You should be able to press fit a bearing into a sheet that thin. To make a hole the correct size, get the exact size of the bearing, then subtract a few thousandths for the press fit, and make a hole exactly that size. Usually this requires using a reamer, or CNC machining.

Re: Press Fit
 

WE would be getting this laser cut, does that make a difference?

Re: Press Fit
 

This year we had our chassis water-Jet. There was no problem press fitting into it when i made the hole the exact size. NOTE: we also had it painted so that may have affected it). But when we got our off-season Chassis laser cut it was also press fitted and stayed perfectly (wasn't Painted). you shouldn't have a problem with 0.09", as long as you have a support all around the outside of the sheet-mteal and bearing, so that the metal doesn't bend. we had that happen, but we just hammers it back in place :/

Re: Press Fit
 

Your would have to find out the kerf (width of cut) of the laser, and try to compensate accordingly.

You might run into problems with eccentricity of the circles being cut, and/or the accuracy and repeatability of the hole itself. Maybe try to get some samples cut and see if it's sufficient.

But the easiest method would be to just cut them undersize on the laser and then ream them as squirrel suggested. Anything that requires a precision fit should be drilled undersized and then reamed or bored to the final diameter.

Re: Press Fit
 

"A few thousandths" is FAR too much interference unless you have a really big bearing. Ideally, you're looking for something in the neighborhood of 4 ten-thousandths undersize for that size of bearing. You can get special undersize reamers to do press fit bores.

Let me ask, why do you need a press fit anyhow? In FRC, they're often more trouble than they're worth. Just make a good close slip fit and use part geometry to keep everything in place (flanges, shoulders, counterbores, snap rings, etc).

Re: Press Fit
 

If the hole is just a little too loose sometimes you can make the hole smaller by whacking the edge of the hole with the ball end of a ball-peen hammer. That will result in a little bit of the edge sticking into the hole creating a slight interference.

ChrisH

Re: Press Fit
 

If you are looking at thin sheet (.062 or less) be aware that Flanged bearings sometimes have an undercut at the flange. It is possible that a hole of "proper" size is loose because the sheet falls into the relief groove.

Laser cutters and water jet cutters tend to have compensation for cutter kerf. You just have to make sure the part program uses the compensation. It would a shame to have nice holes well located by a CNC cutter and then have to try to keep the accuracy with an expensive hand reamer.

Also, look at parts from Spyraflo. These are self clinching self aligning bearings made to go into sheet metal (or thin wall tubing).

Re: Press Fit
 

to elaborate on sanddrag's post for a press fit it is a pretty simple process....look at this chart: http://www.turnedoutright.com/wp-con...rill-sizes.jpg

You select a drill size two sizes smaller than your desired hole size, go one step up to ream out the hole, and then press it on

for example: if I want to press onto a 0.250" shaft, I would go down two steps to a size D drill (0.2460"), then ream out the hole one with one size larger (0.2480"), then press....and you are done

Re: Press Fit
 

Thanks for catching that, I've been working on cars lately....

Re: Press Fit
 

for example: if I want to press onto a 0.250" shaft, I would go down two steps to a size D drill (0.2460"), then ream out the hole one with one size larger (0.2480"), then press....and you are done[/quote]

0.250" is the same as an E drill. D is one size down. Two sizes down would be a C = 0.242"

Re: Press Fit
 

Before CNC this was done in any of several ways, from a file or sandpaper to a lathe with a 4-jaw chuck. It is not necessary for CNC equipment to be used.

Re: Press Fit
 

Getting students to hand size a hole for a press fit bearing...now that would be a neat thing to see! We used to get to learn craftsmanship like that in machine shop class.

Thanks for the added info Don.

Another way to do it is to use a boring head on a mill.

Re: Press Fit
 

You can put a lightly loaded bearing in a .09" plate. If there is a lot of load you would want to use a doubler plate to get more bearing area. The difference from a loose running fit (clearance) to a too tight press is less than a couple thousands of an inch on 5/8" dia. Not a lot more if you are talking about a ball bearing with a OD of 1.125 or so.
Most unpracticed people cannot measure that with a micrometer. Drill tolerance is way more than that. Reaming tolerance is more than that.

What to do?
1) Use a new quality drill bit. Clamp the work well Probably be a little loose. Use bearing mount loctite to take up the clearance. I am not sure how well that will work with thin plate.
2) Drill it undersized and use an adjustable reamer get the right fit.
3) Drill undersize & use a deburring tool to get the right size. Only works with relatively thin bores.

Re: Press Fit
 

he isn't talking a generic drill set, he is talking a real machine shop's drill set where they have the drills accurate to tenths of a thou. An E drill is a generic and it is typically .250, accurate to the thou. If you are pressure fitting with generics... be really careful and take plenty of measurements.

Re: Press Fit
 

All of your bearing fit information (radial ball) can be found in the chart on page 131 at http://catalog.timken.com/WebProject...ookcode=eng11#, with the codes defined on pages 132-145.

If you can't make the holes to the specifications listed there, 0.001" undersized should work. I've found that Loctite Retaining Compound 641 works well in other applications, if you want to make the hole right at the bearing diameter.

As for press fits into thinner materials, I would recommend a flanged or snap-ring bearing with either retaining compound under the lip or 3 screws at 120-degree intervals.

Re: Press Fit
 

fwiw, we made a couple gear boxes this year using flanged bearings and polycarbonate side plates, we discovered that drilling a hole with a Forstner bit will provide a sufficient press fit. There are lots of ways to do things like this.

Re: Press Fit
 

Also note that polycarb cracks when you put loctite on it.

Re: Press Fit
 

This is an area where standardizing in design can make things a lot easier. If you only use a few common sizes of bearings, then you can get the appropriate reamers for these bearings (at some expense, but not awful; and due to design standardization they're used almost everywhere on the robot).

We have a press fit and slip fit (press being .0005 to .001 under depending on the availability of the reamers) for most bearings and bushings we use.

Most 973 robots over the past few years have most gearing running on plates that were waterjetted then reamed out by a reamer in a hand drill.

The reamer is really the best compromise between precision and the ability to use it on any given part and machine. It also allows "fixing" of damaged or out of tolerance parts.

Materials like polycarbonate that are much softer/weaker than the bearing itself will allow a much greater range of bore sizes without undue damage to or efficiency loss in the bearing.

Re: Press Fit
 

There is no twist drill that can create a hole that is accurate within a tenth.

The diameter of the drill itself may be ground more precisely than on a cheapo drill, but the geometry of the tool inherently prevents it from making extremely round/accurate sized holes.

Re: Press Fit
 

In addition to this, any sort of runout on the drill/lathe/mill you are using will compound these issues.

Reamer is the way to go if you want to have repeatable results from plate to plate. Drilling holes, milling them, laser cutting them or waterjetting them will all result in a different sized hole for the same "as designed" size.

The best way to deal with it is to ream.


One understated method of holding bearings in is green loctite (gap filling). Having the bearing slip fit inside a hole, and using appropriate green loctite does a good enough job of holding bearings in.

Also- the ball bearing/ball peen trick is a nice one if youre in a bind. We have a nice 1.5" diameter steel ball bearing. If a hole is a little bit too large, we can just stuff that bearing into the hole and whack it with a hammer. It creates a little curl of material just big enough to bite the bearing and hold it in place.



-Brando

Re: Press Fit
 

On Emperor Swerve we had a 37mm bearing bore that we attempted to waterjet to exact size cutting super slow (like .7 in/min). The walls ended up being nontapered, but the kerf was larger than normal so the hole was easily .002 oversize.

We used some punches and ball peen hammer to rough up both the lip, and the inner diameter of the bore quite a bit in an even fashion around the diameter, and finished the assembly with bearing loctite.

We were able to "fill" that .002" gap in a really high load application with these methods and the bearings still have not loosened.

Re: Press Fit
 

A slightly undersized reamer is definitely the way to go. We've done all kinds of things in the past, but if you want a hole precise to .0001", use a good reamer.

We machined bearing blocks this year on our CNC mill, and some turned out as slip fits, some were press fits. Keep in mind this is the same end mill, same program, same bar of stock. You would think they all come out the same, but there is never a guarantee. Between a bit of high grit (400 or so) sand paper and snap rings, things were easily "good enough" for FRC. But...

Ideally, I would drill it undersize for the reamer and then ream it slightly undersize. Picking the size reamer you want is the hard part, but I would think .0005" under or so would be good enough. Other methods may work, but a reamer is going to give you the closest thing to a true cylinder that you can get.