mini tools
Mini-Lathe 21 tooth change gear.
I received a 21 tooth gear in my mini-lathe upgrade gear stock shipment by error. At first I didn’t know where it could be used. None of the stock gears in a mini-lathe are 21 tooth. (See picture).
The upper 20 and 25 tooth gears are a part of the reversing system. They are small bore with no key way.
The lower two 20 tooth gears in the picture have a larger bore and a 3mm key way. So do the 21 tooth gears I accidentally received. I thought the 21 tooth gear may have something to do with metric threading.
I did some research and I found the identical 21 tooth gear recommended for replacing one of the 20 tooth gears to get closer to cutting certain metric thread sizes. Which one depends on the thread desired. Only one (1) 21 tooth gear is required. Both 20’s are used for some threads.
The mini-lathe because of it’s 16 TPI lead screw can never make all metric threads exactly on pitch.
So the mystery gear is no longer a mystery. The original 20 tooth gears are steel so they are not replaced in my upgrade kit.
Gear Cleaning
I import steel gears for the mini-mill and the mini-lathe. I have sold over 200 sets of gears to people all over the world. Most buyers are machinist, used to working with wire brushes and getting dirty hands cleaning gears covered with grease or a little surface rust. Most carbon steel will rust. However, I show nice shiny gears in the photo’s. My Bad. The real gears have to be cleaned because there is some “gook” used to preserve them from rust while shipping across the salty brine. (Ocean to you land lubbers.)
Most gears are well “gooked” but a few, especially the change gears are only “oiled” a bit light. There is a coating but looks like almost none and as shown here, have definitely gathered some surface rust. The first picture is a worst case gear I could find (65 tooth change gear ). It is the largest in the group and the only one showing rust. It really does look nasty but looks are deceiving.
I think some salty air got into the last shipment. Only one side had this rust and all the other gears clustered in one group on a long bolt with this one had no rust. It is cosmetic and does not make the gear defective.
A spray with WD40, about a 5 minute soak and two to three minutes with the brush shown and the gear is photo perfect. Perhaps too much work for some people with arthritic hands. It is hard for me. A rotary wire brush would do it faster and easier.
I could clean and inspect all the gears, shine them up like shown in the store photos, re-coat with that heavy LPS3 grease for maintaining protection in storage and sell them for about 50% more… Continue reading
MBS115/E Micro-Bandsaw Update
MBS115/E Micro-Bandsaw
I received a question about the Proxxon Micro-Bandsaw MBS 115/E I have in my workshop and used to offer in the store. This is an update after using it for a few years so I thought I should share my reply with everyone (anyone who reads this blog) 🙂
” I like my saw. I use it a lot with the bi-metal cutting blade. I have cut many rather thick (1″) parts (in brass) and cutting 1/8 inch brass or aluminum plate is easy. These parts are for the A3 switcher I am slowly working on.
However, it is a small, light saw that can’t be pushed hard to speed up a cut, as it will stall (no harm so far). The belt rides on a smooth pulley on the blade wheel. The belt cogs only engage the motor pulley, so on the smooth blade wheel the belt cogs reduce surface grip. The motor is also a 1/8 HP, so I assume the belt drive design helps protect the motor. (Proxxon could have put cogs on the the blade wheel but didn’t.)
So I rate it for thin metal and bar stock and detail cutting in the first writeup. I don’t want potential purchasers imagining this saw is a replacement for the cutoff bandsaw and buy one for the wrong use. (Given time with slow feed it could be used but not recommended.)
Original report link: http://thehobbyistmachineshop.com/shop26.html
Low mass saws with aluminum wheels do not have much inertial rotating mass. (stored energy) Same goes with all small aluminum lathes or mills like the Taig and Sherline. These tools can do great work if the user understands the inherent limitations of low mass. Old heavy iron machinist have a terrible time downsizing to mini and micro tool performance and… Continue reading
4″ Mayan in Wax
I use the Mayan calendar as my CNC test program. It is highly detailed and makes the stepper motors really earn their keep. In these photos I show where I have reduced the circle diameter to just under four inches. This is about as small as I can go with this design. I got it off center a skosh. That’s OK, it’s not a keeper. The test is not of the Taig mill but rather the tiny wax profile bit I bought from Bits & Bits.
The bit is 1/8″ in diameter half round with a 15 degree included angle. The end of the tip is 0.005″ It looks and feel like a very sharp needle. The RPM was 10600 (max for the stock CNC Taig) and the feed I had set for 30 IPM. With ramp up it seldom got to 30 IPM except for long paths.
The total run was just over four hours. The Taig and CNC controller took this run without a blink.
I use plain air to clear the wax chips but you can see they still liked to stick around. The problem could be the slow feeds because of the intricate details. I am going to try a faster more aggressive feed on the next Item. I am thinking of trying a small lithophane carved in wax.
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