The Hobbyist's Machine Shop – Blog

"One Perfect Part at a Time"

Exploding a possible myth?

I ran across one of the best reports I have read about the reasons for not using propane or a refrigerant tank for a receiver in a compressed air system. Here is the link in Horn & Whistle Magazine.

I have been in the HVAC business all my life and at first thought all those throw away refrigerant tanks must be good for something. In fact there was at least one manufacturer who was offering a kit to convert these tanks to portable air use. The kit consisted of a valve, gage and a short hose. I used one for several years. This item is no longer marketed.

I have seen air tanks and high pressure (HP) steam vessels that have corroded. All the tanks I have worked with that developed leaks in normal use did just that, developed leaks. They did NOT just suddenly and catastrophically explode. The writer never uses the word “explode” however the term “life threatening” conjures up the impression. I believe the explosion impression makes a good scare story and borders on urban legend.

The “Myth Busters” have shot diver air tanks with bullets and they do not explode. They take off like a rocket.

The expansion and contraction theory presented in the link is a new one for me. It is written as obvious speculation but it does sound plausible. Whether it has caused sudden and complete failure is not substantiated in the article. The fact is the pressure in these tanks in their designed use varies considerably and follows and endures temperature changes from frost on the outside (-40 deg) to 120+ degrees. This too is probably a myth until someone can prove that it has happened.

I am always a skeptic whenever I read this sort of thing. The… Continue reading

Taking care of the little bits.

I did my homework. I looked up the characteristics of 303 stainless steel. Then I had to do a bunch of rather interesting math. Here is the quote that caught my attention:

“Since Alloy 303 will work harden, it should be machined at reduced surface feet per minute and heavier feeds to prevent glazing at the tool interface.”

Circumfrence of a 1/8 inch diameter mill bit, Pi, surface feet per minute (SFM), number of flutes, feed in inches per revolution (IPR) per tooth, rotations per minute (RPM); all figured to the forth decimal. Phew! My math works out to 3361 RPM and 14 IPM. At least that is a starting point. I was using more like 6000 RPM and 5 IPM. Bad Dog!

If that is all geek speak, that OK. I bet you didn’t know machining was a nerd’s job.

Sometine soon I’ll try the new numbers and see how many more 1/8 inch end mills I can break.

My Kind of SHOPing

I worked in the machine shop all weekend. I am trying to make spoked solid steel model locomotive driver wheels on my micro CNC milling machine. They are slightly over 3 ½ inches in diameter.

First I had to make a special fixture to hold the wheel blank onto the milling table. That took all day Saturday. Then I cut the first wheel on Sunday. That took about 7 hours!

I enjoyed the work but am not happy with the current result. I broke three 1/8 inch end mill bits working with the stainless steel. 🙁 I will try carbide end mill bits next if I can find some. The finish on the SS was not what I desire. Standard bits get dull cutting SS.

I have some nice machineable steel to try next and also fine grain cast iron. That will wait until another day and when I have more 1/8 inch mill bits to play with.

It is amazing how time flies when you are having fun. Yes, dear! breaking mill bits is fun… forget about those words I used. 🙂

Outstanding Saw Blade

I bought a premium saw blade to go with my premium PM2000 cabinet saw. I have used many types of power saws in my 60 years but I have just been “blown away” buy this blade on the PM2000. The blade is a Forrest “Woodworker II” and one of the more expensive 10″ blades on the market.

blade2.jpg

The blade doesn’t look it but it is all purpose, both ripping and crosscutting. The carbide teeth are extreamly sharp. I understand the reasons on “teeth set” between ripping and crosscutting. This blade is different. I was wondering about this saw blade with all the teeth the same. So I installed it on the saw.

blade1.jpg

A little “ouch” at the base of the index finger was not from the blade.

I cut some Popular and some plywood I had around. My jaw fell and hit the saw table! No cut noise, no slowdown and no effort. I have never seen a saw cut this well. No splinters, super smooth face on the boards. I could even see the clean open microscopic wood pores on end grain. Boards can be edge glued right off the saw. This is an amazing blade! It cuts rather than chew through wood. Its like using 40 finely honed chisels to carve through the cut.
The blade can be resharpened about 10 times when required. I have read reports of hobbyist use of 9 years without needing a sharpening. Used properly, this is a lifetime blade. At least for the years I have left!

This blade is a 10!

Taig CNC Ready For Action

I have the Taig CNC mill in place and firmly mounted.

Taig CNC mounted

The mill is now bolted to the bench with three 1/4-20 x 1.5 in. SS bolts (SS to prevent rusting). That is a commercial “bun” pan under the mill. Overall dimensions of the pan are 18×26. I don’t expect the pan to get all the swarf but it will help contain some of the oil and mist coolant when used.

I found what I call “panduit” in a very small size. I mounted it on the back wall to help heep the CNC motor leads up out of the pan. It sure “neaten-uped” the jumble of cable leads.

I am what I considered stage 1 of the Micro CNC install. It is fully operational and I will be using it for cnc projects. Stage 2 will be adding home switchs and end switches. I have some micro switches but I need to design an enclosure for them. Later

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