What type of Drill Rod for Axles?

[Harold_V]

One thing drill rod usually offers, is an accurate ground finish. If the rod is not round, it was not made correctly. Generally speaking, drill rod is made with a ground finish with a very specific diameter.

Unfortunately, that's not necessarily true.
As has already been mentioned, drill rod isn't always round, and it isn't always in spec. The reasons why make no difference to the guy who makes a purchase and discovers the issues after the fact. And, it should be noted that simply measuring with a micrometer will NOT disclose a three sided condition, which is actually quite common.

If you've ever operated a centerless grinder, you fully understand the problems already mentioned. Something as simple as starting with a piece of stock that isn't dead straight creates issues that can be overcome, but if they're in the hands of an individual without a clue, it rarely ends up that way. It's the nature of the machine---which relies heavily on the skill of the operator to produce round and straight parts.

H

[SteveM]

And, it should be noted that simply measuring with a micrometer will NOT disclose a three sided condition, which is actually quite common.

The reason for that is that as you rotate the measurement around the part, the diameter will be consistent as you will be measuring from high spot to low spot or some variation that always gives the same diameter.

You can use one of these

or I think you can put it in a v-block and rotate it with an indicator on it.

Steve

[rkcarguy]

I've used stress-proof in most of my projects, but I've always used pillow blocks of some sort as well. Not sure what I'd use if my axle was to be a wear surface for a needle bearing.
I've posted this before, but I feel a needle bearing is a poor choice for our application. The small diameter wheels spin faster @7mph than a cars wheel on the freeway, and the speed is way too fast for such tiny little needles. They are typically used on things that pivot, not rotate, or for instance the floating side of a centrifugal clutch or motorcycle clutch basket(only has to spin at ~idle until the clutch locks up).

[WJH]

I've used 1018 CR only to have it warp like a banana after each end was machined

[FKreider]

Hello All,

Thank you for the comments, I wasn't aware that drill rod has a chance of being out of round, good to know!

This was in reference to 3/4" scale engine designs with brass or cast iron "plain bearing" axle blocks.

It sounds like TGP is the way to go for this application.

[Doug_Edwards]

I've posted this before, but I feel a needle bearing is a poor choice for our application. The small diameter wheels spin faster @7mph than a cars wheel on the freeway, and the speed is way too fast for such tiny little needles. They are typically used on things that pivot, not rotate, or for instance the floating side of a centrifugal clutch or motorcycle clutch basket(only has to spin at ~idle until the clutch locks up).

I pulled out my Torrington catalog on needle and roller bearings. A 7/8 dia axle with a 3/4" long bearing has a limiting rpm of 5500 rpm. The basic capacity of the bearing is 3600 lbs. If you run this bearing at 5500 rpm with a 6" driver, you would be traveling close to 100 mph. How fast did you want to go? Fwiw, if you use a similar roller bearing, the limiting speed would be over 300 mph!

I'm using needle bearings in my Climax trucks. I figure I will not be running more than 5 miles an hour, although the limiting rpm is close to 7000 rpm. I put hardened bushings on the axles for the bearings to run on. The bearing load was over 1000 lbs per bearing. I think I am covered. I Used 1045 ground and polished shafting for the axles and lineshafts.

Regards,

Doug

[Steggy]

Hello All,

Thank you for the comments, I wasn't aware that drill rod has a chance of being out of round, good to know!

This was in reference to 3/4" scale engine designs with brass or cast iron "plain bearing" axle blocks.

It sounds like TGP is the way to go for this application.

If you can get your hands on some StressProof TGP, that would be ideal. StressProof undergoes a series of cold drawing operations that results in exceptional straightness before the TGP process. The end piece is very straight, very round and very smooth, almost like glass.

The attached photo is of one of wheelsets for my F7. The hazy stuff on the axle is anti-seize compound.

Axle made from StressProof TGP

[pat1027]

What effect does the out of round drill rod have? I looked up tolerances on drill rod out of curiosity. ALRO lists concentricity within .005".

[rkcarguy]

I've posted this before, but I feel a needle bearing is a poor choice for our application. The small diameter wheels spin faster @7mph than a cars wheel on the freeway, and the speed is way too fast for such tiny little needles. They are typically used on things that pivot, not rotate, or for instance the floating side of a centrifugal clutch or motorcycle clutch basket(only has to spin at ~idle until the clutch locks up).

I pulled out my Torrington catalog on needle and roller bearings. A 7/8 dia axle with a 3/4" long bearing has a limiting rpm of 5500 rpm. The basic capacity of the bearing is 3600 lbs. If you run this bearing at 5500 rpm with a 6" driver, you would be traveling close to 100 mph. How fast did you want to go? Fwiw, if you use a similar roller bearing, the limiting speed would be over 300 mph!

I'm using needle bearings in my Climax trucks. I figure I will not be running more than 5 miles an hour, although the limiting rpm is close to 7000 rpm. I put hardened bushings on the axles for the bearings to run on. The bearing load was over 1000 lbs per bearing. I think I am covered. I Used 1045 ground and polished shafting for the axles and lineshafts.

Regards,

Doug

I would question the 5500 rpm, is this greased? Oil bath? Size of the needles? A bearing with larger needles more in line with a Timken would certainly hold up better. I am curious though, and would like to know what the needle bearing size is that you are using. I'll calculate out the RPM of the needle based on the diameter when the axle is going 5500 rpm and we'll see how far into the stratosphere it is.
Another issue is that needle bearings have next to nothing for tolerance for torsional twist, so if your trucks or chassis is twisting at all as you navigate uneven track, the needle bearings are going to fail in short order.

[rkcarguy]

.005" concentricity is terrible by the way.

[Doug_Edwards]

I've posted this before, but I feel a needle bearing is a poor choice for our application. The small diameter wheels spin faster @7mph than a cars wheel on the freeway, and the speed is way too fast for such tiny little needles. They are typically used on things that pivot, not rotate, or for instance the floating side of a centrifugal clutch or motorcycle clutch basket(only has to spin at ~idle until the clutch locks up).

I pulled out my Torrington catalog on needle and roller bearings. A 7/8 dia axle with a 3/4" long bearing has a limiting rpm of 5500 rpm. The basic capacity of the bearing is 3600 lbs. If you run this bearing at 5500 rpm with a 6" driver, you would be traveling close to 100 mph. How fast did you want to go? Fwiw, if you use a similar roller bearing, the limiting speed would be over 300 mph!

I'm using needle bearings in my Climax trucks. I figure I will not be running more than 5 miles an hour, although the limiting rpm is close to 7000 rpm. I put hardened bushings on the axles for the bearings to run on. The bearing load was over 1000 lbs per bearing. I think I am covered. I Used 1045 ground and polished shafting for the axles and lineshafts.

Regards,

Doug

I would question the 5500 rpm, is this greased? Oil bath? Size of the needles? A bearing with larger needles more in line with a Timken would certainly hold up better. I am curious though, and would like to know what the needle bearing size is that you are using. I'll calculate out the RPM of the needle based on the diameter when the axle is going 5500 rpm and we'll see how far into the stratosphere it is.
Another issue is that needle bearings have next to nothing for tolerance for torsional twist, so if your trucks or chassis is twisting at all as you navigate uneven track, the needle bearings are going to fail in short order.

Question it all you want, but the numbers come straight out of the Torrington catalog. If you are interested, I pulled the numbers from data for bearing number BH-1412. I looked but did not see any mention on the size of the needles in the bearing. I would guess for this bearing that they are 3/32 or 1/8. The catalog makes no mention of oil for lube, only grease.

From my notes it looks like I am using the B-812 bearing in the Climax. Basic dynamic capacity is 2130 lbs per bearing, for a total of 25,560. Torrington states if you halve the load, you increase the life by 10 times. My loco weight is 1/50th of the total maximum load. Bearing life is not even a question.

Journal boxes on most locomotives should be able to rock with axle movement. The Climax is no different in that respect, although Climax used more clearance between the journal box and the pedestals that they rode in than what rod engines can use.

One loco that I am familiar with was built in the early 70's with needle bearings on the rods and axles. Over 6000 actual miles with no bearing changes. That is not the only one in the hobby built that way. Hard to argue with success like that.



Regards,

Doug

[rkcarguy]

Doug, I'm not trying to discredit your choice of bearings for your project. There is a lot of posts on here where needle bearing rolling stock trucks are failing and I believe it's from the high speed and lack of the needle bearings ability to self align as the truck sides move. In addition to that, maybe the needle bearings used are tiny and that's why they are failing?

Just to toss out some math for fun:

7/8" axle has surface inches per rotation of about 2.75"
1/8" needle bearing has surface inches per rotation of about .393"

So the 1/8" needle bearing will spin about 7 times faster than the axle, or 38,500 RPM at the axles 5500 RPM max per the manufacturer. That's pretty dang fast, with surface speed of 1,261 feet per minute.