Bump Roller

Here is a quick and useful project for a tool to use on the Mini. It's called a bump roller (Center) and I had never heard of one until I saw a YouTube video with a guy using one.

Basically, if you are like me you have alerted friends and family to keep an eye out for scrap metal you can use on your Mini. Some of the scrap may be pretty rough or may have been out in the weather for a while so when you chuck them up to clean them up they are very difficult to get reasonably centered in the chuck before you start your clean up. This little tool will help you do that.

With a little bit more research on the web I found bunches of designs, then came up with my own that fits the Mini and an A2Z tool post. Most of the tools I use are 3/8" and set up in holders for that tool height. I wanted my bump roller to not mess with my existing height adjustments and just be able to remove the existing tool and set the bump roller in and tighten it up. The other thing I wanted it to do was be an inside and outside tool. That is: the roller close the chuck or farther away depending where the stock was out of shape and how much stock is needed for the job.

This is what I came up with.

The holder is made from a piece of 1/2" square, steel stock and about 3.5" long, some 608ZZ skate bearings (8x22x7 mm), 3/4" long 8-32 SS flat heads and some washers for race bearings. You can see in the picture below that I offset the screw hole on this end by 3/8" from the top and from the bottom on the other end and both are inset from the ends 1/4". This puts the center line of the bearing at center line of the stock in the holder and leaves the main roller out enough to contact the stock yet not interfere with the square stock. WhaaLah, no height adjustment necessary.

Why two washers? I didn't want to cut down the screws nor drill and tap any deeper into the square stock. I tapped into the stock about 3/8". Keep in mind I made this on the fly with no drawing.

So if your are like I was...How do you use this thing? It's pretty simple but takes a bit of practice and care, because it's a bit unsafe to do. You chuck up the piece to be centered lightly and run the roller...very carefully into the piece until the bearing starts to spin and you will see the piece true up. Stop the lathe and tighten the chuck. In the YouTube Video he does a surface touch down to .0005-.001. It was amazing and works! Also GadgetBuilder made a fancy one that fits directly on his tool post...but he obviously has a mill and he calls it a Bump Center which may be more appropriate.

My first piece was a 1/2"x 3' Copper plated brass. It had been an electrical ground rod my son in-law gave me from a job he did. It was really crusty, corroded and bent a bit, but knew there were some good parts in it. The first time I tried to true a piece, it had to turn it down to 3/8" to get it straight and clean. After using the bump roller I was able to salvage right at 7/16"...just below the copper plating.

Here are some pictures in the QCTP with a piece of the Plated Brass in both positions.

This Bump Roller (Center) is a great addition to your Mini's Tool Kit that can made in an hour or so. Check out the links and Have fun!