Mini Mill Solid Column Conversion

The original design Sieg Mini Mill( sold as Harbor Freight, Grizzly, Little Machine Shop, Micro Mark, and others) featured a tilting column that few people used.  The pivot point and the relatively thin column allowed for a considerable amount of flex in the machine. I found this especially troublesome when using a boring head, for its single cutter creates a highly unbalanced load.  I could only take very light cuts, or the column would flex.  Fortunately, Little Machine Shop has been working with Sieg to improve their products sold under LMS' Hi Torque brand.  First they enlarged the table significantly, then they replaced the motor and noisy gears with a more modern design. That left one area to improve, the flexible column.

 The new solid column is not just the old column with the pivot removed, but an entirely new and much heavier casting that weighs 11 pounds more then the old one.  28 vs. 17.  That is a huge 64% increase in weight.  The weight is in additional wall thickness.
      At left is the original column, where they apparently tried to make it as thin as possible.

Here is the new solid column, with wall thicknesses about double the original, and a substantial mounting flange cast as one piece, rather than bolted on as before.

 Since there is much less space inside the column, I had to trim the head of the bolt holding the gas spring in order to get it to fit inside.








The solid column comes with mounting holes for the Hi Torque electronics, which mount differently than the Harbor Freight electronics.  At left is the unpainted HF column, showing the mounting holes, and the painted Hi Torque column below it. I drilled the new column to match the HF, see below.  I also drilled a hole for the gas spring conversion.

Since I had everything apart, and I am now aware of the added stiffness of the solid column, I decided to add a spacer to the head which extends the head out 19 mm and moves it up 20 mm.  I made the spacer from a piece of 3/4 inch aluminum.  It has 4 tapped holes and 4 clearance holes.  The spacer bolts to the front half of the head, and then the rear half bolts to the spacer.

This mod uses the 4 original 8 mm socket head cap screws and 4 hex head bolts, 8 mm x 35 mm.

Spacer bolted to front half of head.

Rear half of head is then bolted to spacer.  This picture shows all that is left of my original Harbor Freight mini mill.  Everything else has been replaced with parts from Little Machine Shop.  Even this remnant of the HF machine has 4 significant mods:
Belt drive conversion.
Gas spring kit
Spring loaded spindle lock
And now my spacer.
Still to be done is the relocation of the fine feed knob. Eventually this will be replaced by a ball screw Z drive.
What does the inside of a mini mill head look like?  Here are some pictures:

The intermediate gears are no longer used. I left them in place, but locked their position so that they are disengaged from the main shaft.

 

The rear half of the head showing the pinion gear.

The finished machine. It is a vastly different mill than the original Harbor Freight mill.

I put the machine through its paces and while it was much improved, it still had some head shake under heavy loads.  Even though I had the gibs very tight, when I placed my finger so that I was touching the head and the column at the same time, I could feel the difference in vibration between the head and column.  This meant the head was moving against the column. Unlike the gibs for the X and Y axis, where the forces are mostly pressing the sliding parts together, the head is hanging from the dovetails on the column.  This means that the four 6 mm setscrews are supporting much of the load, and their contact area is very small.  I added a fifth setscrew, and milled smooth recesses in the back of the jib where the setscrews press against it.  This solved the problem, and my DRO no longer changes its reading when I tighten the lock..

One thing I did not expect when making the conversion is that the column is moved nearly 2 inches forward on the solid column base.  Here is a photo of the two bases showing the location of the column on each.  With the pivot assembly gone, Sieg was able to move the column forward where the pivot used to be.  While this would not be a problem for most users, the column now interfered with my 4 inch vise, which I had machined to clear the pivot.  I decided that the easiest solution was to change back to the tilt column base and make an adapter to fit the solid column to it. I wanted my adapter made from cast iron for the same reasons machinery is made from it.  It has good wear and vibration dampening properties.

I scoured my local scrap yard for a suitable piece of cast iron and found something with nearly perfect dimensions for the job: A 10 pound barbell weight.  At about 8 inches in diameter and nearly an inch thick, it required a minimum of machining to transform it into an ideal adapter.  First I surfaced both both sides to get them flat and parallel to each other. Then I cut it square and drilled the holes.  I also had to machine a step in the bottom to match the step on the base.

 Prior to machining the step, I milled the top of the base flat.  This part of the casting was smoothed with body putty, a trick Chinese manufacturers have been using for years.  I milled the surface down until I had clean metal, then I machined the step in my adapter to match.




I then bolted on my adapter and drilled the holes for the 8mm column mounting bolts into the base.  I drilled these 14mm deep to accommodate 50mm long bolts. After the holes were drilled, I removed the adapter and applied JB Weld to the rear surface of the base, and reassembled it.

  I did this because I wanted the adapter and base behave as one piece when I tapped the holes, and while torquing down the column.

After the JB Weld cured, I tapped the 8mm holes for the column and assembled the machine.  The column is now moved 0.85 inches toward the rear compared to a stock solid column mill.  This is not as far back as the location of the tilt column due to the fact that the solid column has a flange in the rear.  However, it is a big improvement over the location of the stock solid column machine.

That created a new problem.  The rubber bellows no longer reached the column, so I made a bracket which clamped to the column dovetail and shortened the distance the bellows needed to stretch.

 A setscrew in the side provides the clamping force in the same manner that jib adjusting screws work.

I lowered the mounting point to give the Z axis stop a place to rest that is below the surface of the table.  The original bellows mounting screw holes can be seen above my clamp.

Here is the Z axis stop in its resting position. Here it does not interfere with my vise, the end of which is visible on the left.

I believe the finished machine is at least as good as a stock solid column mill, and has some advantages. The additional clearance of 0.85 inches may not seem like much, but on a small machine like this, it is significant.  My spacer in the head increases the throat depth by 0.75 inches over the stock machine.  The combination of the tilt base and adapter plate is very rigid, with the 8 pound plate solidly attached with 7 bolts.  This is a viable alternative for those who want the advantages of the solid column without having to discard their perfectly good base.

Holographic LCD reflector

Over 20 years ago, Dupont developed a clever polymer that could be used to create holograms.  One promising application was a reflective backing for LCD displays.

While in theory any color could be created, green became the dominant color because the human eye is very sensitive to green, and because holograms are created by using high power lasers.  Argon lasers were the predominant high power lasers back then, and they are very good at producing green light at 514nm.  The hologram at right was made with a 514 argon laser.

The holographic reflector appears 6x brighter to the eye than does the traditional silver background.  This is because the hologram directs most of the light towards the viewer rather than distributing it widely like the silver diffuser.


It is easy to add the holographic reflector to any LCD.  This weather radio came with the usual dull gray background. I disassembled the radio and peeled the silver diffuser off the back of the LCD.  Then I attached the hologram to the LCD using a transparent adhesive film.

Here is a Fluke multimeter that I modified, next to an unmodified one. The contrast between the modified and original radios was even greater.



Unfortunately, the idea never caught on.  Casio used it in some digital watches like this one, but I know of few other commercial applications.

Update:  A reader has supplied the following additional information:

Found your post on the DuPont holographic films. Nice descriptions and details. I was quite involved in the project. A correction if I may, the brightness enhancement films did catch on in a big way! Almost all of the Timex watches for 3-4 years, almost all of the higher end Motorola cell phones for 3-4 years, and many other applications. What ended the growth was the introduction of full color LCD's.
Doug




The diagram at left illustrates how this works.
Unlike a normal mirror which reflects light away at the same angle it is received, holograms can be designed to reflect light at any angle.  This property can be used to great advantage by reflecting ambient light at a different angle than the glare reflecting off the surface of the LCD display.
In the diagram, the glare from overhead light is reflected down, away from the viewer, while the green light from the hologram is directed towards the viewer. The result is the brilliant, high contrast display shown above.



 I have a few square feet of the stuff, and convert most  of my LCD displays.

Like most holograms, this hologram is a picture of something.  In this case, it is a picture of a ground glass plate illuminated by 2 laser beams from the same laser.  The hologram reflects light at the same angle that the laser beams were at when they illuminated the glass plate.  We would then make a master hologram from which copies could be made.
At right is a sheet of copies.  This picture was taken in a brightly lit room, but the holograms were so bright that the room appears dark.  one neat attribute of holograms is that they are nearly transparent.  Here is the exact same sheet when looking through it at the overhead lights that previously made it glow bright green. 

We tried other colors with limited success.  Here is a blue one.  Not nearly as effective as the green. The bright objects in the background easily wash out the weaker blue.

By combining red, green and blue lasers, we made some white ones.  However, even those did not perform as well as straight green, which can be seen shining  through the white one.

Finally, here is a picture of some scraps.  They only glow when viewed from the proper angle.  The ones that appear dark are pointed the wrong way.

 Years ago, someone had the idea of chopping these up and putting them into paint.  A good idea, for unlike dyes, holograms never fade.  Unfortunately I don't believe the inventor got very far with his idea.

One idea that DuPont and some automakers invested a lot of time in was a holographic center stoplight, or CHMSL, as it is known in the industry.  The idea was that a hologram in the rear window would glow red when the brakes were applied, but otherwise would be transparent.  While it worked, it had no real advantages over traditional stop lights.
Another, better idea was a transparent television set.  When not used, it appeared to be a somewhat foggy, but generally clear, window.  When turned on, the picture was quite good.  One idea was to use it to display advertisements in store windows, then let people also see inside.  Unfortunately I have seen little of that idea since then.

Kohler K341 Engine Overhaul

 After 35 years of reliable operation, the Kohler engine in my John Deere 316 was beginning to burn a little bit of oil.  About a quart every 3 or 4 hours.  So, I decided to overhaul it and bought a kit which included a new piston, connecting rod, and valves.  Step one was disassembling and cleaning the parts. The engine was much dirtier on the outside than on the inside.
I stripped everything out except the main bearings.  Since most of the bolts were oil covered and a little loose when I removed them, I cleaned every bolt and their corresponding holes.

How do you remove the cam?  The cam rides on a shaft that is about 1/4" diameter.  It goes in the black hole to the right of the crankshaft hole in this picture.  Drive the shaft out from this side with a soft punch.

This is a solidly built engine, and weighs somewhere around 90 pounds when assembled.  Once disassembled, the bare block was easy to pick up and turn over to clean. Surprisingly, every internal part measured equal to new specifications. With the exception of the piston and rings, there was no measurable wear on the crank, camshaft, cylinder bore, and valve lifters. This was good news in that it was not necessary to bore the engine and use an over-sized piston.

The camshaft shaft will come out of this hole. You should not have to hit the other end of the shaft very hard.

The valve guides also had no measurable wear.  I have no idea of the total time on the engine, only that I put on 400 hours since I bought it in 2002.  Since the tractor had signs of considerable wear when I bought it, I'm guessing that it had about 1,000 hours on it, so maybe it has 1,400 total.

This engine does not have the balance gears present in some versions, and from what I've read, generally discarded by engine overhaulers.


I decided to replace the governor gear, even though like everything else, there was no wear visible.  However, the gear is plastic, and I once had an 18 HP Briggs & Stratton self-destruct because it's plastic oil splashing gear failed.  Since a governor failure could result in a destructive overspeed, I felt it was a good idea to change it.

However, that greatly complicated the rebuild, since I had to remove the camshaft to access it. As you can see in the picture on the left, it is located deep inside the engine, above the camshaft. Removing the camshaft requires removing the bearing plate, along with the crankshaft.

There was no sludge inside the engine, and the
oil pan was one of the easier parts to clean.

The front main bearing. these massive ball bearings were in great shape.

Finally, the fun part.  Reassembly. Here is the camshaft installed, and note how the governor gear is not even visible anymore.

The timing marks are hard to see.  Here is a view through the fuel pump opening.  The tiny dot on the cam gear lines up with the line cast into the crankshaft.
 These pictures were taken with my iPad, which has an impressive ability to selectively focus exactly where you want it to.  The iPad was also useful for reading the rebuild manual.

 The crank and connecting rod installed.

The alternator coil and bearing plate.   Once again, this engine was very tight, and I had to use all three paper spacers to get proper clearance between the sides of the bearings and the crank.
The book specifies 35 ft-lb for the bolts holding the side plate, so I torqued them to 35, and one of the bolts snapped, while I could feel another stretching. Fortunately, I was able to remove the broken bolt without difficulty. However, I was bugged by this, for I then realized that the soft bolts used were only good for around 24 ft-lb.

I decided to replace all the bolts with high strength bolts and torque them to 35 ft-lb.  Since the overhaul manual is about 15 years newer than my engine, maybe they upgraded the bolts. In any event, if your engine has bolts like the one on the left, with the recessed top, don't torque them to 35.  Better to throw them out and buy new ones.

With difficult jobs like this, any help is welcome.  Well, almost any.  I had just installed the flywheel when my feathered friend jumped on top of it.  She is a very social chicken, and is always nearby.  But this surprised me. She spent a few minutes inspecting my work before jumping down.

I installed the engine in the tractor with only the flywheel attached.  Not having an engine lift, I wanted to keep it as light as possible.  It was also easier to torque the head when the engine was solidly bolted down.

The head had a huge amount of carbon, but I don't believe it was ever removed for cleaning.
It polished up nicely.

The new piston and valves.

The engine started right up, and ran well.  It has 6 hours on it now, and appears to be breaking in properly.

The entire job took about 24 hours from first removing the hood of the tractor, to reinstalling it.

The original piston.  Badly scored by carbon which had built up on the cylinder wall.  This was the only part in the engine that showed serious wear.  This piston design is no longer used, and the newer one has the piston rings located higher up.  That should reduce the amount of carbon that can get trapped above the rings.

The original connecting rod.  It was good enough to re-use, but a new one came with the rebuild kit.

The original valves.   Some erosion can be seen on the exhaust valve stem, but otherwise they were in good condition.

Alaska Kodiak coal stove

 I use an Alaska Stove Co. "Kodiak" model stove for my primary source of heat.  This solidly built stove is made from 1/4 inch steel plate and cast iron hardware.  I believe these were made beginning in 1977, the year Alaska Stove was founded. Unfortunately, Alaska Stove no longer makes this model, or anything similar to it.  Their new stoves are all stoker-fed rice coal burning stoves, while this is a hand fired stove that will take nut coal or larger, as well as burn wood.  Unlike rice coal stoves, which need electricity for both the stoker and a draft fan, this simple stove requires no electricity.  Yet, it will run 12 hours unattended, giving it nearly the same convenience as a stoker stove.  And it is remarkably uniform in temperature over that time period.  The stack temperature typically stays within a range of 300F to 600F, and the hot air produced within a range of 150F to 200F.

 I received the stove without documentation or an outer shell.  However, it was clearly designed to have an outer shell, for the 1/4 inch plate on the top and rear have cutouts along the edges to create air passages.  I made a shell out of 4 inch concrete block.  The block shell creates an airspace around the outside of the stove which efficiently heats the air circulating through it while also making the stove much safer, for the block rarely gets hot enough to burn someone.  Two 8 inch ducts are connected to the shell.  The inlet has a fan to help circulate the air throughout the house.  It is a small fan which moves about 600 cubic feet of air a minute, but it runs continuously.  This way the house temperature is always uniform. The above picture shows the top of the stove and the air ducts. When the picture was taken, the air was exiting at 145 degrees.







To measure the flue temperature, I use an antique Wheelco thermocouple galvanometer.
This solidly made precision instrument is probably 75 years old and was used in an oil refinery.  It, and thousands of other valuable old items were slated for destruction in order to reduce the refinery's taxes.  This one escaped destruction, but still wears the yellow paint of death.   I cannot find any record of Wheelco.  It is unfortunate that this fine example of American engineering is nearly forgotten, due at least in part to tax laws that encourage the destruction of assets.

 After using the stove a few times, I realized that while it is a very good stove, it also had some serious shortcomings.  When shaking the grates, it was impossible to shake them without having coal jam in between them.  It was also too easy to go too far and dump the coal.  I lengthened the link between the grates until it hit the sides if the grates were rotated more than 15 degrees.  This has proven extremely effective.  The shock of the link hitting the sides loosens the ash and makes it fall readily, while it is impossible for coal to drop down and jam in between.

  Then there was no ash drawer.  This was a serious shortcoming in a stove that is over 2 feet deep.  Also, the ash door is surprisingly small.  I couldn't do anything about that, but I did make a drawer as big as I possibly could.  It has about 1/4 inch clearance all around.  This was a huge help, but there remained one problem.  Because the drawer was narrow, some ash fell along the sides.  This had to be shoveled out.  I took the stove apart and removed the supports for the firebrick. I drilled and tapped holes into them and bolted sheet metal ash guides to them. This gets about 80% of the ash that missed the drawer. 

   

 One problem with coal is that it takes a lot of air and a very hot fire to get it going, but once it is going, it needs only a small amount of air. In fact, I only open the main air door when starting, and then close it.  The stove then gets all the air it needs through the small openings in the ash drawer, and even these I have open only about 1/4 of the way.  I should point out that I have a very strong draft up my 25 foot chimney.  Since the coal burns so uniformly for 8-12 hours, an automatic control is not necessary.

Recently I added a safety feature: An automatic closer for the main air door.  Without that, I had to say close to the stove when starting, a process that may take more than a half hour.  Coal can surprise you, for it may smolder at a low burn for a while, until it reaches critical mass.  Then you can see stack temperatures approaching 1000 degrees F in a matter of minutes. Not a safe situation.  My safety system consists of an electromagnet which holds the door open, and a thermocouple controlled alarm with relay contacts.  When the alarm trips, the alarm cuts power to the electromagnet and the door drops by gravity.  I like this because it is fail safe. If the power fails, the door will drop.  If the thermocouple fails, the controller will alarm and the door will drop.  Still, I  consider this a safety backup only and would not intentionally leave the house and depend on the alarm. However, I could someday forget and this little thing just might save my house.  Here are some pictures:


The temperature controller:  An old Omega controller from my junk box.  Also in the box is a Sonalert audible alarm and a 9 volt "wall wart" power supply from some long ago discarded electronic gadget.

 The electromagnet holding the door open.  The electromagnet is another "wall wart" transformer, but this one has had one side cut off to turn it into an electromagnet.  Transformers make decent, and cheap electromagnets, for nearly everybody has some of these laying around somewhere.  This one was from a US Robotics 33k modem.  Remember those?  They were popular when nearly everybody was using dial up America Online.  As an electromagnet, this transformer uses only 63 milliamps at 9 volts.

 The electromagnet has de-energized, and the door dropped.  While the power is restored to the electromagnet as soon as the stove cools and the alarm stops, the magnet is far too weak to raise the door.  In fact, it has barely enough power to hold the door up.  Better that way.  Any disturbance would cause the door to break free and drop. 
 The arm that holds the magnet is attached to the stove bracket by a single bolt which is aligned with the air door hinge pin.  This way the magnet can be set to hold the door at any position, or even swung up and out of the way.

I believe Alaska Stove still sells replacement grates for these stoves. At least they did 6 years ago, when I replaced mine after acquiring the stove.  This stove was badly abused and seriously over-fired, warping the grates and the firebrick supports along the sides.  The front was warped too, and  the door would not close properly.  Since Alaska Stove did not sell the firebrick supports anymore, I had a local foundry cast new ones for me, using the old ones as a pattern.  I straightened out the front by intentionally over-firing it without firebrick in the front.  Then I pounded the warped front with a sledgehammer while the steel was soft.  That worked well, and the door closes properly now.

I built a 6 foot x 18 foot coal bin that holds approximately 10 tons.  Later I covered the bin with solar panels, in the process creating what may be the worlds only coal bin with solar panels.















I burn between 3 and 4 tons of coal each winter, at a cost here of $200/ton.  That is like getting heating oil for less than $1/gallon, or propane for maybe 75 cents.   However, the money I'm saving by burning coal is only part of the story.  My house is much warmer with coal heat.  My high efficiency propane heater delivered all it's heat upstairs to the living spaces, as it was designed to do.  This however, left me with a frigid basement which was unpleasant to be in during the winter months. By contrast, the coal stove heats the basement to 80 degrees F.  This heat eventually works its way upstairs, supplementing the heat arriving through the ducts.  Because of the stored heat in the basement, the stove can be out many hours before the house feels cold.  By contrast, when heating with propane, the house only felt warm when the heater was running.  Yet, even when running the propane heater for maximum efficiency by turning the heat down whenever possible, I still had some January propane bills that were larger than my entire season when heating with coal.