Workshop
Do You Need The Balls?
There is a common conception in the amateur machinist world that ball or roller bearings are always the preferred selection to bushing or solid surface bearings. That is not always the case. Machine engineers, of all people, should know it always depends on the application. There are many applications where ball bearings are contra indicated, meaning they should not be used. Some of those reason can be as simple as cost over performance, excessive noise or the possibility of bearing contamination in harsh environments.
The primary benefit of using a ball bearing over other types is the greatly reduced drag due to its small rolling surface contact point. Their use is preferred when low friction is a high priority and other factors like low noise is not. They will reduce power requirements, help reduce friction heat and provide long periods of operation. If they are properly sealed, they will reduce maintenance. The best, high quality ball bearings can reduce run out and take thrust loads. These are worthy goals but sometimes are higher goals than necessary.
To quickly get to my point, I’ll examine the bearing needs for the lead screws on all the axis of a small manual mini lathe. First, do radial ball bearings “increase machining (position) accuracy” on any of the calibrated axis including the Z axis main feed screw over a bushing type bearing? The answer is an absolutely no.
This is because the linear slide position accuracy is a function of axial (not radial) screw loads affecting the amount of compression/expansion of the lead screw, drive nut thread engagement, drive nut mounting rigidity, thrust surface material and screw shaft bearing end play. This as combined is commonly called backlash. Minor drive screw side play (run out) is not a factor.
Radial bearing loads… Continue reading
Cutting Slots
I present a few more action shots on the X3 mill. The DRO is wonderful for cranking in the proper cutting dimensions even after a careful layout. The layout marks confirm the location but the caliper like accuracy of the DRO makes sure the cut is exact.
These parts will be used to braze up the coupler pocket for the A3 tender. I am not showing all the work involved, just some of the unusual. The saw here is the same thickness as the brass plate. I am cutting two layers at the same time. That way opposite sides will be exactly the same. The pieces will be assembled like an egg crate.
The cuts are made on one side of the vice but unseen inserted on the other side of the vice is more brass material the same thickness. This is to keep the vice clamping equal so that it doesn’t “rack” when tightened.
I will be posting more pictures of how the coupler pocket is assembled and finished.
Sine of 45
I know most of my readers like action shots. Here are a few to keep the juices flowing. It’s just one very tiny step in the making of parts, but there is a bit of interesting machine set up going on here.
I had to cut a 3/32″ wide x 45 deg. chamfer on the one end of both of the two brackets I made for the tender steps. That doesn’t sound like much of a job, does it?
I priced 45 degree end mills and after I got back off the floor, I decided that wasn’t the least expensive way to run this job. At least for the two tiny cuts I needed to make. A file might work but it would look like… well you know, the smelly stuff.
I dusted off the sine vise and although it seemed like massive overkill, it wasn’t all that hard to set up. The fun part was I was able to do a little math and I actually like math. The reason it is called a sine vice is the height of the spacers (called sine blocks) is the sine of the angle desired times the distance away from the hinge.
Here I wanted 45 degrees, and the sine of 45 is sin(degrees(45)) = 0.70710678. I used o.707 as close enough. I have a 4 inch sine vice so the stack of blocks needs to be 0.707 x 4 = 2.828 inches. You can see that number on the top of the pink notepad in one picture. I rounded to 2.830 just to make it easier to build the stack and still be plenty (over) accurate for this task.
Two 1.000 inch, one .700 inch, and one .130 inch block does the job. The actual machining seemed trivial as it usually does. 🙂
Another Project Finished
Yes-sir, completely scratch built from raw ore. NO, not likely. Ha!
This is a little repair project my daughter gave me. It is a ball head for a camera (photography) mount. The bottom of this device screws down on a tripod or studio steady mount.
There is a quick release on the top that is attached to the camera.
The handle bolt is loosened to adjust the angle of the camera and that is where the problem was. There are internal splines in the original handle that were stripped out. It would no longer turn the locking bolt to secure the ball from moving.
I learned all about these spring loaded handles and also how the ball mount itself works in this little project. There are two main types of these handles. Most of us know the “pull the handle to adjust position” type. I have a lot of them on my machine tools. There is a second type called the “Safety” handle where the user must push in against the spring load to engage the handle. That is what I have here. The handle pops back out and drops to a safe position when not engaged.
So the project was mostly selecting the correct replacement handle. However there was a catch. There is always a catch, right? The end of the original bolt was drilled out and a pin with a tapered cone inserted. It is this cone against an internal ramped surface that pushes up and locks the ball movement.
The machining chore was to drill out the end of the new handle bolt to fit this tapered cone pin. The challenge was to hold the bolt for drilling (without disassembling the handle) and drilling the hard end of the bolt deep enough for the pin to insert.… Continue reading
It’s The Little Things
The small bits and pieces are going to get me. All home machinists know the purchase of the major machines is the big money decision in getting started. No doubt about that. But there is something more insidious to my available funds.
What gets me after the big purchase is the constant cash flow required in getting all the little bits and pieces I need to get projects completed. It’s not really any different than any other hobby. All my other hobbies I enjoy seem to be cash eaters too. Maybe I should take up whitlin’ if I can find some free wood.
I was just sitting here at the computer ordering a few restock parts from McMaster-Carr. I am updating my starter and countersink drill bits both 60 degree and 82 degree. They generally last a long time but mine have seen better days. I’m getting a five piece set of each angle. I need a couple of #2-56 taps, two because I’ll break the first one. With two I won’t break either. That’s the way it works, I know.
OK, throw in some #2-56 flat head machine screws, only a few bucks…
What happened? (!!) That total can’t be +$80.00! Wow, its right. My theory is correct. It’s the little things that bite me the hardest.