Recommendation? Threaded rod or not for contact wheel?

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gudspelr

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Jul 1, 2013
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I’m FINALLY making more progress on my surface grinder attachment for my KMG. I’m to the point that I need to mount my 3” serrated contact wheel to the 1.5” tool arm and then I can figure out the best placement and angle for the rail, etc. I’m finding myself at a mental block for how I want to attach the contact wheel.

Originally, I planned on some all-thread and was going to tap the hole in my tool arm. But, the 1/2” rod has just a bit of play when slid through the bearings on the wheel. Which made me think I’d get some 1/2” cold rolled steel, thinking it would be a better fit inside the bearings. But, should I thread part of the rod and tap the tool arm? Should I leave the rod smooth and just thread the ends? Would only have to worry about drilling a perpendicular hole and not about threading it perpendicular as well.

I feel like this isn’t as hard as I’m making it, I just don’t want to mess up the tool arm or end up with an out of square hole.... I have a G0704 I plan on using, but also trying to figure out if I should use drill bits and get a reamer or if a 1/2” end mill will leave me a round hole. As you can tell, I’m not a great machinist... :). Thanks for any help and/or suggestions you have.

Jeremy
 
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If you have drill pres i would tap the tool arm..Make sure that drill press is square and drill hole for taping .Start taping on drill press.... One note , even if thread is not 100% square IF you use totally flat shims/washers /spacer they will correct that .There was slightly give? in thread so.....when you tight bolt spacer will seat FLAT on tool arm .Often mistake I see is that many use stamped washers for spacers which is not good and then they wonder why tracking is not good ...on perfectly build grinder .
There was are bolt on exact dimension , not like ordinary one make search .
 
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gudspelr said:
Originally, I planned on some all-thread and was going to tap the hole in my tool arm. But, the 1/2” rod has just a bit of play when slid through the bearings on the wheel. Which made me think I’d get some 1/2” cold rolled steel, thinking it would be a better fit inside the bearings. But, should I thread part of the rod and tap the tool arm? Should I leave the rod smooth and just thread the ends? Would only have to worry about drilling a perpendicular hole and not about threading it perpendicular as well.
Jeremy
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That will not be problem , when you tight nut/bolt wheel will spin on race of bearing so that play no matter .
 
A 1/2" grade 5 bolt should fit properly in the bearings, without any play. Check the bore to make sure it's correct, 1/2" = 1/2", unless the bearings are an off-size metric measurement. Drilling & tapping into the tool arm should be fine with a drill press or mill.
 
I agree with noseoil ... use a grade 5 or grade 8 bolt that fits the bearings. Pick a length that allows a clean shoulder for the bearings to ride on. Threaded rod is not an exact size and will cause problems.
 
Thanks for the suggestion. I’ll take the wheel over to the hardware store and see what I can come up with for a bolt that’ll work. If for some reason that doesn’t seem like it’ll work, maybe I’ll get the 1/2” steel and go from there.


Jeremy
 
The clearance between the threaded rod and bearing doesn't really matter, because the bearing isn't rotating around the threaded rod. The outer race of the bearing rotates around the inner race, and the purpose of the fastener is to immobilize the inner race.

If you really want to have near-zero clearance, you need a shoulder bolt or a precision shaft. Measurements of a 1/2" bolt are below:

Bolt diameter at threads: Ø0.492"
Bolt diameter at unthreaded portion: Ø0.497"

In my opinion it's a bit silly to say that 0.008" clearance (the difference between 0.500 and 0.492) is too much but 0.003" clearance is ok. If that clearance really mattered, then both 0.003 and 0.008" would be too much.
 
Thank you for your thoughts. I asked myself how much is too much, not really knowing the answer. I also wondered if the tensioned belt would more or less hold the wheel steady and remove that play between the rod and ID of the bearings. I don’t think I’d be this “worried” about it, except it’s for a surface grinder attachment...and thousandths add up. Will be curious to see if a bolt will help/have noticeably less play.

Jeremy
 
Did you read previous post ? That PLAY don t exist when you tight bolt , bearing don t spin on bolt ! You will need press to move wheel :) Get bolt or threaded shaft ....tight it and don t worry about that anymore........... Even smaller then 1/2 inch Dia. bolt would done job .
 
Sorry, but I disagree with that last statement. The wheel needs to be centered pretty closely to be concentric. Even .005" would create a wobble and vibration as the wheel moved in and out during each revolution.

I agree with P.Brewster that a shoulder bolt will work fine ( which is what I recommended). However, P.Brewster was giving the dimensions of a bolt and the OP asked about using threaded rod ... which is much less precise ( which I stated).

Anyway, we all are talking more or less the same thing in that a 1/2" shoulder bolt will work fine.
 
If your contact wheel has a crush sleeve between the bearings, you can probably tighten it enough to eliminate play. Without a spacer between the bearings, you might not be able to tighten it enough to prevent wobble. I don't think it would be a big deal with a 3" diameter wheel unless it is horribly balanced. I have a 12" wheel from aliexpress and it wobbled a lot at high rpm because of the play on the bolt. After I mounted it more rigidly, the vibrations were greatly reduced.
 
Stacy ??
I can use 8mm Dia. bolt on 12mm inner dia .bearing and that wheel will NOT wobble ,will spin like shampion :)Wheel SPIN on inner race of bearings ...period !
Think about that again.......
 
Hubert S. said:
If your contact wheel has a crush sleeve between the bearings, you can probably tighten it enough to eliminate play. Without a spacer between the bearings, you might not be able to tighten it enough to prevent wobble. I don't think it would be a big deal with a 3" diameter wheel unless it is horribly balanced. I have a 12" wheel from aliexpress and it wobbled a lot at high rpm because of the play on the bolt. After I mounted it more rigidly, the vibrations were greatly reduced.
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Why should anyone make wheel without spacer between bearing ???????????
 
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Guys.................................this bearing spin TRUE .......regardless of off center hole for bolt ,capishi ?
9HKRnFM.jpg
 
Natlek said:
Why should enyone make wheel without spacer between bearing ???????????
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Natlek, you are right in theory and you could have an eccentric hole and the bearing might spin perfectly true. Of course, in that world, all wheels are perfectly balanced (why would anyone make wheels that are not?) and you don't even have to tighten the bolts all that much. Most likely, that is not the reality the OP is dealing with. That's why I thought I would mention my experience with contact wheels without crush sleeves. Capisci?
 
Natlek is correct as long as the wheel is clamped down hard against the inner races ... and there is a through spacer to prevent the races from moving inward under the pressure.
I still would use a shoulder bolt anyway.
 
Stacy E. Apelt - Bladesmith said:
Natlek is correct as long as the wheel is clamped down hard against the inner races ... and there is a through spacer to prevent the races from moving inward under the pressure.
I still would use a shoulder bolt anyway.
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I just look what you call shoulder bolt...............with that bolt ,seeger ring is enough :) And cost for right 1/2 inch bolt is around 3$ :D
 
Well, I took the wheel to the hardware store and grabbed a 1/2” grade 8 bolt. Once they’re long enough, only the ends are threaded, leaving the rest of it a full 1/2”. It fit nicely in the wheel and was noticeably less sloppy than the all thread rod. I was able to thread more of the bolt when I got home so it’ll go through the tool arm and have enough threads to adjust the “tightness” of the wheel.

I’m planning on drilling and tapping a test hole in the end of the tool arm so I can see how square I am before doing it at the correct place. Once I get the wheel attached, I’ll figure out where to attach rail system. I’ll need to mill down some of the tool arm though so the rail will line up with the wheel. Thanks to you all for your halo and advice.


Jeremy
 
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