Best economy bearings for drill rod?

[Lionclaw]

As I read through wood mill build logs, I see lots of different bearing/drill rod combinations.

I want to use 3/4" drill rod for my Z rails. I've tried searching enco, msc, and mcmaster and I can't really seem to find decent bearings that aren't in the $30/pc range.

Does anyone have any suggestions? I'm sure I'm missing something. I don't mind changing away from 3/4" drill rod if necessary.

[ger21]

Try these at Mcmaster Carr. 6673K15 on page 973. You may need hardened shafts, but 18" 3/4" shafts are only $19 each. page 958 12" are only $12.65

I just checked, and drill rod is ±.001, so it won't work with those bearings.

4 bearings and 2 - 18" shafts would be about $85. I spent $110 on ebay for 4 3/4 ball bearings and 18" shafts. A few months later I got a set of 18" THK's on Ebay for $40. If you're patient, you might find a similar deal. But, it may take months.

[pminmo]

Depending on tools available, drilling acetal (Delrin) or UHMW is used a lot. Neither is real expensive and it machines easily. With a drill press and a set of cheap forstner bits you can accomplish alot.

[Lionclaw]

Thanks Phil and Gerry. Good bits of advice.

[OCNC]

Originally Posted by Lionclaw As I read through wood mill build logs, I see lots of different bearing/drill rod combinations. I want to use 3/4" drill rod for my Z rails. I've tried searching enco, msc, and mcmaster and I can't really seem to find decent bearings that aren't in the $30/pc range. Does anyone have any suggestions? I'm sure I'm missing something. I don't mind changing away from 3/4" drill rod if necessary.

Look at this thread. Steve (spalm) seems to have worked out an inexpensive solution to this problem.

[Mcgyver]

the ultimate in economy would be sintered bronze bushings but you'd have better luck with ground shafting

[pminmo]

The cheapie bronze bearings in my experience fit well on drill rod. In all honesty, I've bought maybe 6 pieces of drill rod. My measurement capability is with one of the cheap digital calipers. .0005 resolution, claim .001 accuracy. I've beat it against 1 2 3 blocks, feeler gauges and a cheap .001 dial caliper. The all agree with each other. Each piece of drill rod has been dead nuts on. But I can't say I have had any luck with parallel bronze bearings (yet). I just bought a 12" x 18" granite surface plate (page 28 of the sale flyer), a 12" dual beam height gauge and an optical center punch(page 30 of the sale flyer). I must say I really impressed with the optical center punch. Both the optical center punch and surface plate were on sale at KBC tools. www.kbctools.com

[Lionclaw]

Lots of good info, thanks guys.

I think I'm going to try precision ground shafting with oilite bronze bearings.

The shaft is -0.0005 to -0.001 and the bearings are +0.000 to -0.001.

It's a bit of a gamble, but if it doesn't work out I can always try different bearings. But for less than $30 out the door, I think it's worth a try.

Final decision is whether to go with 3/4" or 5/8" shaft. Any suggestions?

-Andy

[Mcgyver]

Originally Posted by pminmo The cheapie bronze bearings in my experience fit well on drill rod. In all honesty, I've bought maybe 6 pieces of drill rod. My measurement capability is with one of the cheap digital calipers. .0005 resolution, claim .001 accuracy. I've beat it against 1 2 3 blocks, feeler gauges and a cheap .001 dial caliper. The all agree with each other. Each piece of drill rod has been dead nuts on. But I can't say I have had any luck with parallel bronze bearings (yet). I just bought a 12" x 18" granite surface plate (page 28 of the sale flyer), a 12" dual beam height gauge and an optical center punch(page 30 of the sale flyer). I must say I really impressed with the optical center punch. Both the optical center punch and surface plate were on sale at KBC tools. www.kbctools.com

Before they put the dials on 'em, people called 'em verniers...but machinists called them very-nears They just will never be as accurate as a micrometer. It sounds like you are trying to empty the kbc warehouse, but with all this precision stuff you are collecting consider a good Starrett or Mito micrometer. They easily will help you measure to less than a thou.

When you use an oilite (sintered) bearing, lets say 1" OD, the bearing will be a few thou larger than 1". Thats because its supposed to be an interference (press) fit into an accurately size hole (easily done with a reamer). its all engineered such that when its pressed in, it is compressed and the ID gets smaller. Machinery's Handbook will show the calculation, and how you can actually control the clearance you get by the size of the bore

problem with oilite (sintered) bearings and drill rod is that drill rod's tolerances are over/under, where as precision shafting will always be under. If your reamer is cutting slightly over and the stars line up, the drill rod may fit, but as often as not it can be slightly (2 or 3 tenths) over - this is enough to wreck the fit and enough that you'd see it with a good micrometer. also, drill rod is not hardened, not as good a finish and not necessarily round.

it works for some people, perhaps because the reamed hole was a thou oversized or whatever, but these are the reasons drill rods a less expensive, but not ideal material for this application.

Lionclaw, I have no idea why your bearings are under sized?? measuring small bores can sometimes present challenges - how sure are you that its -.001??

[Lionclaw]

The tolerances I listed were just those on the mcmaster product descriptions. I'll double check to make sure.

Edit: Linking isn't working. Here are the part numbers from McMaster:

Bearings - 2938T19
Shaft - 6061K34