Bearing Reamer?

[asid61]

Originally Posted by InFlight

An experienced mentor machinist with a Starrett micrometer can achieve half a thousand on a nice big lathe that well is adjusted.

An above average student machinist on a mini-lathe using $15 digital calipers would be good to hold 0.002".

My point was either end of the machinist spectrum could take a 1.125 mill or drill and undersized it enough to achieve a snug R8 bearing fit.

I can get to half a thousandth without too much care on the small Taig that the woodshop teacher owns. If one is using a good pair of Brown and Sharpe calipers or Mitutoyo, those hold to 0.0005" easily. Of course, maintaining a "good pair" of quality calipers is difficult in a student's hands. Ironically, I find that using a telescoping gauge and micrometer is harder for me than just trusting the calipers, although either method isn't impossible.
Back when we used to use the boring head, all measurements would be taken on the B&S calipers, well before I was on the team. They were able to get reasonably good presses on bearings, although I don't know what the skill level of the people were before I was there.
That being said if I tried to get that tolerance on steel, I wouldn't have much luck.

Drilling a 1.125" hole with a drill bit I would try to avoid. Using an endmill will get those tolerances but a drill bit won't hold the tolerances easily unless you drill undersized by 1/64" or something first, and even then I'm not sure. The largest hole I have drilled in metal was with a 7/8" drill bit, and that did not go as well as just using an endmill of the same size. What is your method to make sure it works correctly?

[InFlight]

Most 1.125 drills have a 1/2" shank. You simply can put that in a 1/2" collet and use it in your mill.

[RoboChair]

Originally Posted by InFlight

An experienced mentor machinist with a Starrett micrometer can achieve half a thousand on a nice big lathe that well is adjusted.

An above average student machinist on a mini-lathe using $15 digital calipers would be good to hold 0.002".

My point was either end of the machinist spectrum could take a 1.125 mill or drill and undersized it enough to achieve a snug R8 bearing fit.

My students could hit 0.001" easy with any lathe we have(maybe not the Grizzly) my experienced lathe students could hit that +- 0.0005" most of the time with a few pointers. But really reamers are the way to make it easy, you can make your own for cleaning up holes if you have patience, spare time, and some tool steel.
My favorite "bugdet" calipers by the way are a $35 pair of Fowler digital calipers from Amazon

Originally Posted by s_forbes

I don't think that this is what you're looking for, but we used this step drill bit to clean up bearing holes in our waterjetted pieces this past season. It can put a 7/8" OD hole into 1/8" thick material, or run through thicker material with a 1.125" OD hole. Just the right size for the 3/8" and 1/2" bearings we all use.

http://www.mcmaster.com/#8841a35

Step drills are cheaper than reamers, but they can wander if you are taking off a lot of material. Our gearboxes worked great, but we had padded in an extra .003" between adjacent bearing holes to prevent gears from binding if things were off. If you want tighter tolerances, you probably don't want a step drill.

I will second the step drill method! It's super fast and easy and in my opinion is SO worth the $45 or so it costs. It will post size your holes and will be solid as long as you use positive retention like rivets or retaining compound.

My personal favorite method for making a 1.125 hole in aluminum has to be a Carpenter's Spade Drill. I am dead serious here. It probably won't be fantastic for gearbox plates but with a little time on the grinder to modify the bit it will make a press fit hole every time. The only major limits on this method is it can't go through much more than 0.125 thick material and nothing tougher than aluminum. You should never try and do this by hand, not really for danger reasons, it just won't work. Your puny meat fingers aren't as stiff as a drill press. Below is roughly what a modified spade bit looks like.


If you don't believe me watch AnthonyDV drill a hole and hand press a bearing in.
https://youtu.be/yIonCvyEFks?t=29m40s

[InFlight]

There seems to be a misconception of the accuracy that can be achieved on an average small or mid-size lathe with a 3 Jaw Chuck.

Most three jaw chucks have some run out, not holding the work perfectly centered. You can measure this run out easily enough, and it will be much larger than 0.0005 on almost all lathes. This is not much of an issue if you don't move the work, and use a cut-off. As soon as you move the work in the jaws, or use some of the chucked length you will introduce inaccuracy.

Extreme accuracy requires use of a collet work holder, well-adjusted gibs, a very stiff tool post, and quite accurate measuring tools.

[asid61]

Originally Posted by InFlight

There seems to be a misconception of the accuracy that can be achieved on an average small or mid-size lathe with a 3 Jaw Chuck.

Most three jaw chucks have some run out, not holding the work perfectly centered. You can measure this run out easily enough, and it will be much larger than 0.0005 on almost all lathes. This is not much of an issue if you don't move the work, and use a cut-off. As soon as you move the work in the jaws, or use some of the chucked length you will introduce inaccuracy.

Extreme accuracy requires use of a collet work holder, well-adjusted gibs, a very stiff tool post, and quite accurate measuring tools.

Runout != diameter tolerances. Although getting concentricity with a round face is affected by the runout, the bearing press fit diameter is not affected.
The freshly rebored taig jaws had around 0.0003" of runout, and have probably increased to beyond that since I last redid them.

[FrankJ]

I use a step bit most of the time. If the hole is a little big, I peen the edges. I use positive retention to locate the bearing so I am not depending on the press fit to do that. I had not thought about polishing the bit to make it a little smaller. Large dia twist drills tend to end poorly with sheet metal. When they grab, they will bend the sheet metal.

[Fusion_Clint]

Update,

I went ahead and bought one of these, I got it from toolstoday for $31.00

http://www.amanatool.com/products/ro...nch-shank.html.

Today we started making a custom single speed transmission for our first WCD chassis that we are working on during the off season. We cut our bearing holes 0.01" undersize with our CNC router.

Then we used this router bit, in our old manual mill for the final reaming of the bearing holes at approximately 800 RPMs. Plate was 0.25" thick 6061 T6 aluminum.

It worked perfectly, I'm pretty sure it will stand up to long term use, time will tell. But for $31, it is a cheap and reliable way to finish your bearing holes for a press fit.

[asid61]

Good to know! Did you take any measurements of the final diameter? How tight was the press?

[Fusion_Clint]

Originally Posted by asid61

Good to know! Did you take any measurements of the final diameter? How tight was the press?

Did not measure the hole, I will on Thursday at our next meeting. However, I did measure the cutting blades and my Fowler Dial Caliper had them exactly 1.125" apart.

The fit was too tight to hand press the bearing in, but our little 1 ton arbor press put it easily and the bearing spun very nicely afterwards.

V/r