I know I am missing something simple…
I am trying to install some 608zz bearings on a piece of 8mm smooth rod and it won’t fit. I managed to get two bearings on one rod with little problem, it was tight but it fit. When I tried with another piece, I cannot get it to go. The bearings that work on the one rod will not fit onto the others. The OD of the good rod is 7.95~7.96 and the other rods are all 7.97~8.00mm.
It seems the diameter of the rod is a few thousandths of a mm larger that the ID of the bearings. Anyone have any tricks to get them to fit. I am thinking of sticking the rods in the freezer overnight to see if it will shrink enough to fit while cold, but I doubt it will work.
The only other thing I can think of, is to get more rods/bearings and try to get a working combination.
Polish or sand down the rod by spinning it in a drill while holding the sand paper against the rod.
@Wayne_Friedt That’s a good idea. I’ll pick up some fine sandpaper or emery cloth tomorrow and see if I can get it to work. Thanks!
If this is stainless rod you’ve made a mistake. You want chrome rod, made on a cylindrical grinder. I made the same mistake once and I still have 16 metres of stainless rod in my garage. Because it work hardens you’ll never get it ground down unless you do it by hand with sand paper on a lathe. Each rod will require hours of work. If you try to grind by hand measure very often and be very patient.
If you buy chrome rod it fits first try because it is centerless ground to 1micrometre tolerance. You’re better off throwing stainless away.
The drill is only a good idea if you don’t need the precision of the length. If you just need it to fit a bearing at the end you’ll be sweet, 15 min and you’re done. However if you need an lm8uu to roll on it, my previous comment holds true.
@Matt_Kraemer Thank you for the information. Luckily, I only need to fit a 608zz bearing and a belt pulley on each end. I will not be running any bearings along the length of the rod, so I think the drill and sandpaper method might work. I will test on a scrap piece first, just in case I run into issues.
Thanks again.
If you are using it for a belt idler bearing or an extruder idler you can use an M8 set screw or M8 fastener. M8 drill rod or precision rod will not fit a 608(as you’ve found). The difference is between .1 and .15 mm. For example I just pulled a random stick of rod and a radno bearing. The rod is 7.99 mm and the bearing is 7.88 mm.
SKF recommends a js5 (or h5) rod for light loads on radial bearings like the 608. Which works out to a shaft diameter of 7.997 to 8.003mm for a perfect fit, so any rod smaller than that would likely have too much clearance and larger ones would require some force.
That being said, none of us are using SKF bearings and the Chinese ones are nowhere as precisely made. So if one bearing doesn’t fit, just try another one, it might just have that much more clearance.
Just wanted to update this.
After buying more rods and bearings, I was unable to find a combination that would work. I wound up putting the rod in the spindle of my drillpress and using some coarse, wet sandpaper to trim them down. I kept sizing against the bearings, every few seconds until it was able to slip on. Only took a few minutes each to get a nice fit.
If I had to do it over again, I would use fine sandpaper instead of medium, but I got good results anyhow.
Thanks everyone for your input and suggestions.