Mini Lathe Carriage Saddle Clamp Upgrade - with ball bearings + bonus vinyl cutting project

I know this seemed like a good idea and you are very ingenious working with the tools you have. I'm in the same position. However, I hope no one does this to their lathe. The following information doesn't just apply to bearings but also how tool geometry affects tool pressure and can also be applied to many designs you may come up with for parts or jigs. It's a part of learning machining so I hope you'll keep reading. It comes down to pressure, pounds of force per square inch of surface area (PSI), and simple mathematical principles. Consider the surface area of a ball at the point of contact with a flat plane. Ideally it's an infinitely small area (which would lead to an infinitely large pressure at the point of contact) but practically there is some plastic deformation in the ball and the plane. Let's be generous and say it's 0.01 square inches with only 1 pound of force applied on the lathe carriage. That's (1/0.01 = 100 PSI) at the point of contact. In practice, the force would be much larger. Even a force as small as 10 pounds would apply 1000 PSI at the point of contact. Now, granted, you have more that one ball. However with 5 balls, that's still 200 PSI per ball and the forces are going to be considerably more than 10 pounds. Consider an area of 0.001 square inches, that's (1/0.001 = 1000 PSI). With 10 pounds of force that's 10,000 PSI. With 5 balls, that's still 2,000 PSI per ball. Add to that the fact that the balls aren't rotating AND it's hardened steel against soft cast Iron. The more ball bearings that can freely rotate the better and, as mentioned by others, the bearings should ride against a hardened race instead of the soft cast iron. The point is that the smaller the surface area, the larger the pressure will be. This design will most likely leave dimples and wear a groove all along the ways. Conversely, the larger the surface area, the smaller the pressure will be. That's why the ways are ground flat. The point of scraping is to give a place for a thin film of oil to exist between the 2 ground surfaces, but the surface area is still very large and oil is considered non compressible. It's like having millions of ball bearings.

I am loving these videos!! I just got a 1967 south bend 9" lathe as a high school graduation present, and the sort of beginner projects like thumb screws are just what I needed to learn the ropes!

Love the jaunty angle of the To Motor electrical socket. Gotta build character into stuff. I admire your determination.

Nice Upgrade, looking forward to seeing more!

You got Moxie kid. Most of the guys who criticize you probably wouldn't even tempted to do what you did. So don't take it to heart. You did a good job.

Nice bit of work Tim, I like your innovative approach to problem solving, great work

I appreciate the ingenuity put forth in making the blocks and the bearing assemblies, but I can't help but think that the hardened balls are going to gouge the ways since there is no bearing race to complement them, and there is no way for the balls to really roll instead of grind across the surface. Hopefully I'm wrong.

I applaud your desire to learn. It takes humility and some courage to show your work as you learn. It certainly invites others to want to help in positive ways. Most of these mini lathes have brass plates that slide on the underside of the ways. They're adjusted to be just tight enough to have no play, but not so tight that they have a lot of wear. Brass is used because it slides well on the cast iron, yet is softer than the cast iron so it won't damage the ways. The problem you will run into with your mod, as others have mentioned, is the concentration of pressure the hardened steel balls will put on the underside of the ways. Eventually they'll wear a groove in the cast iron which will require you to tighten them, which will then wear a deeper groove, repeating the cycle. It's unlikely that those balls will roll in their "sockets", but even if they did, they're probably hard enough that they'd still press a groove into the cast iron. More likely is that they'll try to roll, but bill grind against the set screws and develop pitting. The pitting will eventually meet up with the ways and then really do some damage (sharp edges of hardened steel, after all, are what we use to cut metal on these machines). I'd recommend finding some 3mm brass stock that you can place between the balls and the ways. Grind some detents into the brass stock for the balls to press into and sand the top of the brass stock flat and smooth where it meets the underside of the ways. That'll provide a much more rigid setup that won't damage the cast iron and it'll hold its position far longer as well. For making flat surfaces I'd start by watching Dan Gelbart (all of his videos are essentially a requirement for new machinists): https://youtu.be/cwdoUjynpEk

Thanks for the video. You demonstrate how we can upgrade our lathes.

Hi Tim , I realy enjoyed watching all your videos ,it realy gives me a great idea of how to modify and repair equipment and tools ,, tks Pal ..

Always nice to see people make things with the tools they own. Not everyone has access to high end machinery nor is a professional machinist. Weather it works in the long run or not, at least you tried. Good job dude!

Man, you are living dangerously with some of the techniques that you use in the shop.

Great idea to improve stability of carriage. Now the cross slide, these lathes are very prone to chatter due to lack of rigidity

A unique and well executed solution for a common problem. 3ish years later I would like to know how well it has survived the test of time.

well done mate 🎉

I have seen a drill press used as an ad hoc mill. all you might need is a precision table, which you could build. I look forward to seeing the finished product. Good luck 👍

Nice idea. Love to see people having a go at stuff. Not sure ball bearings on way is a gd idea. Some sort of brass adjustable gripper would have been less harsh

Nice upgrade, I just watched a few of your lathe videos, I'm looking to get one after I move, thanks for sharing all the information.

Very good and cleaver job Thancks for share !!!

Nice work. Note the horizontal set screw can inadvertently tighten enough to bias the carrier backward direction can premature wear the V rails on the bed and carriage.