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taydin
04-07-2010, 06:20 PM
I am building a carrying card to carry heavy machinery around the shop. There is going to be a front cart with a handle attached to it and two rear carts. I have bought a type 30218 tapered roller bearing to put under the plate that allows the front cart to be turned left/right. But I am not sure how I should secure the bearing to the mechanism. Here is a picture of the cart:

http://www.taydin.org/web/mcart/on.jpg

Currently, I think I will weld the top plate to the cylinder. The cylinder outer diameter is equal to the inner diameter of the bearing. The top plate will rest on the roller bearing. The bottom of the cylinder will have a groove cut into it and a special ring will hold the cylinder in place. I don't know the correct name for this ring, but it is the kind that is split and has two holes. It can easily be removed and installed using special pliers for this purpose.

This cart is supposed to carry a load up to 2 tons. My question is, will this ring be able to hold the plate securely against the bearing, or should I cut a thread to the end of the cylinder and use two nuts to fasten the top plate to the bearing? The cylinder outer diameter is 90 mm, that's why I'm trying to avoid using a nut.

Deja Vu
04-07-2010, 07:16 PM
Deleted by me...
Getting a phone call while reading/posting can be confusing.

....Sorry taydin

Carld
04-07-2010, 08:43 PM
The retainer is called a snap ring. A thick enough snap ring may hold the bearing shaft in the assembly but I would use a washer with it.

I would rather trust a sleeve on the end with four bolts on the OD holding the sleeve on the shaft. Any side to side swaying of the dolly could break the snap ring or the groove.

Fasttrack
04-07-2010, 08:46 PM
How good are you at welding? How big is the ID of the bearing? Keep in mind that your average roller bearing is not built for thrust loads. You want either a ball thrust bearing or a tapered roller bearing.

That ring you mention is known as an external retaining ring, commonly called a snap ring. They are not designed to handle large thrust loads. If that top plate can sway at all you run the risk of popping the ring. You might instead consider something a little bit more heavy duty, but the ring would probably work.


EDIT - I see Carld types faster... :)

Second EDIT - I need to read better. I see that your taper bearing has an ID of 90 mm or about 3.5 inches for us imperial folks. Now, how big is that top plate? If the top plate is relatively small, than you really have nothing to worry about welding the cylinder to the plate. If you make the plate huge, the lever arm acting against your weld is also huge.

taydin
04-07-2010, 10:24 PM
Some preliminary questions...

What is the weight limit you propose?

The biggest load that these carts will carry is my universal milling machine, which is about 4000 pounds.


What size footprint(s) will the "heavy" machinery have?

It has about 1m by 1m foot and the bottom is completely planar.


Are you sure a single shaft in the middle will be stable?
Do they make affordable bearings that big? .....at least as big as I think you will need such as a "heavy" duty lazysusan type.;)

For the wheels, I used 6204 type bearings, which are rated for about 0.65kN. That comes out to about 650Kg. There are 4 wheels and each has 2 bearings, so the cart should be good for around 5 tons

For the top plate, the tapered roller bearing has a radial load rating of about 19 tons and an axial load rating of about 12 tons. The frame is made using 15mm thick mild steel plates. The top plate is 300mm across and 15 mm thick. The bottom plate is 25 mm thick.

I overdid everything, because I don't have the means to do FEA analysis and such. But this roller bearing mounting seems to be the weakest point, so all the other excess material might be irrelevant.

On ebay, the same type of bearing is sold for 50 bucks, less than what I paid (I paid about 65 dollar here in Turkey)

http://cgi.ebay.com/SKF-Bearing-30218-_W0QQitemZ320511796946QQcmdZViewItemQQimsxZ2010040 5?IMSfp=TL100405196006r4890

taydin
04-07-2010, 10:34 PM
The retainer is called a snap ring. A thick enough snap ring may hold the bearing shaft in the assembly but I would use a washer with it.

I would rather trust a sleeve on the end with four bolts on the OD holding the sleeve on the shaft. Any side to side swaying of the dolly could break the snap ring or the groove.

The bottom of the shaft is going into the base plate, which is 25 mm thick. The groove for the bearing is about 10mm deep, so there is 15 mm thick plate left to hold the shaft in position. But when there is side force, this will try to tilt the shaft over. The 15 mm might not be enough to overcome that force. But part of the tilting force will be absorbed by the bearing itself, because it will be sitting securely in the base plate. hmm... It seems the weakest point will be the snap ring (it will be a 90 mm diameter snap ring. The thickness of the ring is about 3.5 mm) Yes, I think it makes sense to put a sleeve under the base plate, to prevent the tilting of the shaft...

taydin
04-07-2010, 10:44 PM
How good are you at welding? How big is the ID of the bearing? Keep in mind that your average roller bearing is not built for thrust loads. You want either a ball thrust bearing or a tapered roller bearing.

I'm am between newbie and average in welding


Second EDIT - I need to read better. I see that your taper bearing has an ID of 90 mm or about 3.5 inches for us imperial folks. Now, how big is that top plate? If the top plate is relatively small, than you really have nothing to worry about welding the cylinder to the plate. If you make the plate huge, the lever arm acting against your weld is also huge.

The plate is 300mm diameter. I made it large so that it can provide a wider support for the milling machine foot. There are going to be 3 carts under the foot, so there is a slight chance for the machine to tip over in the diagonal direction. The wider top plate is supposed to prevent that, or so I hope.

I looked into buying this type of set, but the prices were around 600$. I think I will be able to make my own for around 200$. When you factor in the learning and the fun, it will be a pretty good deal :)

darryl
04-07-2010, 11:23 PM
You're going to weld parts, so you'll want to make sure the bearing will still fit the cylinder after the weld is done, and (harder to fix) that the bearing will still fit into the pocket in the lower plate after that's welded in place.

Personally, I would have gone with a real thrust bearing instead of the tapered roller.

taydin
04-08-2010, 05:09 AM
You're going to weld parts, so you'll want to make sure the bearing will still fit the cylinder after the weld is done, and (harder to fix) that the bearing will still fit into the pocket in the lower plate after that's welded in place.

Personally, I would have gone with a real thrust bearing instead of the tapered roller.

After welding is complete and the part has cooled off, what will happen to the cylinder? Will it have expanded or contracted? How about the pocket in the base plate?

John Stevenson
04-08-2010, 05:27 AM
Don't worry about the snap ring or the other issues, just make it as shown.

All the forces are bearing down onto the thrust bearing, in practice there is virtually no side forces otherwise it would be hard to push.

I have some 7 tonne machinery skates here where the top isn't even fastened to the dolly, just relies on the depth of the cup and weight.

In use you will be more concerned about the load coming off the skate than the skate bending sideways, if there is enough force to bend a skate sideways you will have pushed the machine into the next county by then.

Black_Moons
04-08-2010, 06:03 AM
I know you allready bought the bearing, but did you ever consider a more typical arrangement like 2 cheap radial ball/roller bearings a few inchs apart and a roller thrust bearing at the bottom?, while requireing 3 bearings, they would likey only be $10 each due to being subject to MUCH less stress and stresses only in the axis they are explicitly designed for.

winchman
04-08-2010, 06:26 AM
I bet you could find some front wheel unit bearings off a truck that would carry the load and avoid all the problems with machining/welding precision parts to mount the bearings. They're usually replaced before they're completely dead, so scrapped unit bearings likely will be free for the asking.

Like these from a Yukon:
http://images.channeladvisor.com/Sell/SSProfiles/13000043/images/23/515053_515054_chevy_gm_hub_bearing_assembly_BR9304 17.jpg

http://images.channeladvisor.com/Sell/SSProfiles/13000043/images/23/515053_515054_avalanche_silverado_sierra_hub_beari ng_assembly.jpg

There's an earlier thread about them:
http://bbs.homeshopmachinist.net/showthread.php?t=40135

Regardless of what kind of bearing you use, I'd put some small rollers around the edge of the turntable for added insurance.

taydin
04-08-2010, 06:40 AM
I know you allready bought the bearing, but did you ever consider a more typical arrangement like 2 cheap radial ball/roller bearings a few inchs apart and a roller thrust bearing at the bottom?, while requireing 3 bearings, they would likey only be $10 each due to being subject to MUCH less stress and stresses only in the axis they are explicitly designed for.

I had actually first bought a thrust bearing (a 50311 I think) :)

But I returned it because I wasn't sure how to handle the side force issue. The thrust bearing with the two radial bearings holding the shaft is a great idea.

The only downsize is that it will have more height (to accommodate the thrust bearing, two radial bearings and any washers, snap rings etc... But I will keep this one in mind...

I am also looking into getting another 30218 and mounting them back to back. But that will get expensive, so I am leaving this as a last resort.

taydin
04-08-2010, 06:46 AM
I bet you could find some front wheel unit bearings off a truck that would carry the load and avoid all the problems with machining/welding precision parts to mount the bearings. They're usually replaced before they're completely dead, so scrapped unit bearings likely will be free for the asking.

There's an earlier thread about them:
http://bbs.homeshopmachinist.net/showthread.php?t=40135

Thanks for the pointer. I will ask about at the junk yards...


Regardless of what kind of bearing you use, I'd put some small rollers around the edge of the turntable for added insurance.

Ok, but then I would need to place a plate underneath the top turning plate so that the rollers have a surface to roll on. But it would definitely make the cart much more rigid and that's the most important thing. The milling machine is very top heavy, so I want to avoid any shaking because of elasticity, otherwise it will just tip over :eek:

Black_Moons
04-08-2010, 07:27 AM
you could use the tapered bearing + a normal radial roller bearing

Or even use the tapered bearing to draw a shaft down (preload) a giant lazy susan (thrust bearing).

winchman
04-08-2010, 11:13 PM
For something like this, I'd consider making a thrust bearing using two rings of 1/2" round bar with short pieces of 1/2" pipe on short spokes between the rings. A hefty pin in the center would keep the rotating upper plate from shifting.

darryl
04-09-2010, 01:32 AM
Maybe going off on a tangent now- I once made a couple of thrust bearings using garage door springs- the type that sit horizontally above the door. I cut a few rings off the spring, did a little bending to get the ends of each ring to line up naturally, then epoxied each ring into a groove in a backing plate. That was followed by a toolpost grinding to get flat and smooth faces, then I made a ball retainer disc to control as many balls as I could get to fit around the rings.

Basically, this is a thrust bearing with flat faces and not grooves for the balls- the faces being made of spring steel and the balls obtained from a bicycle store. I think the rings were about 3 inches in diameter, or 3 1/2- the balls were 3/16. Each assembly got to be nearly an inch high, which was a bit much, but it worked. I have no idea of the load carrying capacity-

What it has reminded me of though is castors- there's a thrust bearing, and a wheel to boot! Some of those are capable of bearing (sic) a lot of weight. You could cut some length off the ears where the wheel mounts onto, and arrange to either weld or bolt these to your dollies.