Ball bearing space into piece?

[J_Nichols]

Sorry if this is not the correct place to ask this question, but I'm designing a circuit to control the speed of a small motor.
If I've a ball bearing of 10mm of diameter and I want to fit it in a straight piece of plastic... How many mm should has the hole in the plastic to be able to fit it?

 

[Joe G]

If the od of the bearing is exactly 10mm, the hole would be 0.3937" for a perfect fit (will be a press fit). I'd make it a bit over for a slip fit. too small of a hole and the plastic may split if the wall is thin. The standard fit would be -0.0002" to 0.0006" for a plain ball bearing.
Do a search on bearing slip fit, press fit, running fit. also look for machinist web sites.


also the type of plastics would make a differance, teflon will "give" a little, where as acrylic will not give and will crack.

 

[KMoffett]

Depends on how tight you want the fit.
10.0838mm with a X drill
10.2mm with a 10.2mm drill
10.2616mm with a Y drill
10.3188mm with a 13/32" drill
and so on: http://bobmay.astronomy.net/misc/drillchart.htm

Note that drills usually produce slightly larger holes than the stated diameter.
\Ken

 

[KeepItSimpleStupid]

My crystal ball doesn't have a clear pic of what the OP wants.

Usually we talk of shafts having a slip or press fit. Although I've worked din the English system 0.001" under and 0.001" over are fro press and slip fits. Round holes are reamed with a reamer and say 0.499" 0.500" and 0.501 reamers are available for 1/2 inch.

Then again, I can picture a single "ROUND" ball 10 mm in diameter and a flat plate (of who knows what thickness) that this ball sits on for whatever reason.

Something like a golf ball sitting on a golf tee except the tee is flat. Dunno. Xtal ball broke?

 

[dr pepper]

When drilling a hole for accuracy drill a couple of sizes smaller then size below, then the actual size.

If your building a ball bearing motor then the actual size isnt all that important, 11 or 12mm would work.

 

[jpanhalt]

Here's my $0.02

Of all the comments, I tend to agree with those of JoeG and KISS. Here's are few additional comments/suggestions:

1) First, you do not say what type of plastic you are using. That can be important for several reasons. "Drilling" hard acrylic or polycarbonate can be a lot different than drilling PVC or a similar soft plastic. Second, if the hole is a little oversize, different plastics will respond quite differently to acrylic glues and space fillers, such as Loctite or super glues. I would suggest not using such acrylics, unless you are sure they are compatible with the plastic. Some safe alternatives to consider are water-based white glues and yellow carpenter glue (both basically PVA), polyurethanes like Gorilla glue, or Goop (E6000).

2) Second, drilling that large a hole with a conventional 2-lip twist drill can be asking for trouble. In many plastics, it will tend to hog in and cause cracking or a very not-round hole. You can modify the drill bit so it scrapes rather than cuts into the plastic. Grind the acute cutting edge so it meets the plastic perpendicular (sometimes called dubbing the drill).

3) Depending on how thick the plastic is, a two-lip drill will wobble quite a bit. A one-lip, step drill might give you a better result (one brand name is Unibit). You can also drill a pilot hole and then use a counterbore to get a nice hole. For a good fit to a bearing, I usually bore the hole, rather than drill the hole, but I assume you do not have a mill or similar tool for boring. I would recommend that you at least use a drill press, regardless of whether you use a standard drill, step drill, or counterbore. And, be sure the piece you are drilling is held well to the table. It is very likely to grab on you.

John

 

[KeepItSimpleStupid]

Good points John!

To add to what John said, Plastics can be cooled with water and dish detergent while drilling. I also agree that the plastics can basically "grab" the bit and pull it through. Pilot Point bits work nicely. For large holes like 1/2 or 5/8 you can grind your own pilot point bit, but it's not for the faint of heart.

I learned early. In high school I had to learn to grind my own bits because of a project I was doing. Later in life I had to grind a "contour bit" for a lathe.

 

[throbscottle]

I read on a case modding project site that the way to drill holes in plastic (I think it was perspex, specifically) is to drill some concrete first with the drill you intend to use - if you don't have a specialist bit, that is.

O/P if you have spare plastic, try a few different methods, see what works best. Good luck!