Saturday, March 30, 2013

Building My Own Gingery Metal Lathe

Building a metal lathe based on the following David Gingery's books:

The Charcoal Furnace
The Metal Lathe

Difficulty Level (Easy, Medium, Hard, Insane):

When I started doing some research about aluminum casting I came across a series of books which were written by David Gingery back in the 80s the first of which dealt with the aluminum foundry concepts. In the second book he's using the foundry to build himself a metal lathe.

Back about a year ago I figured it's pretty neat and I decided to try building one. However, after about 50 hours or so I kinda lost interest and other more urgent projects came up so I put the lathe on the back burner. When Melanie kicked me out of the house and told me to go to the shop and enjoy the last two months of my parental leave in January 2013 I figured I might as well start on restoring my 1949 ducati cucciolo moped I inherited. However, I needed a sand blasting cabinet first, so I built one. Then I needed a polisher/buffer, so I built one, then came the need for a metal lathe so...yes, you guessed it...I built one. This post is about my lathe project.

I never knew how complex a metal lathe really is. Essentially, it's a very sturdy and precise tool that turns metal around one axis. Then, there's a cutter that is mounted on a carriage which can move left/right (x-axis), in/out (y-axis) and any combination of the x and y axes (yes, the plural of axis is axes).

Instead of explaining it all in words, I'll have plenty of pictures with a description of each step below.



This picture was taken from wikipedia to list the parts of the lathe carriage
1: Tool post
2: Top-slide
2a: Top-slide feed screw and dial
2b: Compound portion of top-slide
3: Cross-slide
3b: Cross-slide feedscrew and dial
4: Saddle
5: Apron
5a: Carriage hand wheel
5b: Half-nut lever
5c: Feed lever

Wood pattern for the bed using Gingery's dimensions
Support Foot for the bed using Gingery's dimensions
The mold for the bed
After the bed was cast
After the bed were shaken out
Second try at the bed casting; the first one was warped and unusable
Looks better now
The support feet for the bed and a set of vise jaw chucks
The support feet with the sprues cut off
The assembled bed with support feet
I realized that this was going to be way too small for what I wanted so I decided to up-scale Gingery's dimensions to make it wider and longer.

The up-scaled pattern for the bed support feet
The up-scaled pattern for the bed, 4" wide, 24" long
The bed pattern in the cope of the sand mold
The drag portion of the sand mold of the bed
Separating the cope and the drag of the bed sand mold was a real challenge
I had to use a car jack on one side and a hydraulic separator on the other side because the sand mold weighed about 60 lbs and it had to be lifted perfectly vertical so as to not damage the mold cavity. This took a long time and about 4 tries to get perfect.
The other side of the bed mold
And then after 3 hours of work I poured the aluminum just to find out I had forgotten to cut the in-gate (about 1/2 by 1/2 inch in the sand mold) so it didn't fill the cavity it was supposed to but instead leaked out of the mold. I was SO mad!!!
The "art" that cost me 3hours...
For the next attempt I didn't pour the aluminum fast enough so it created mis-runs. Another 3 hours gone!
And then I finally cast the first full part just to find huge shrink cavities. Another 3 hours down the drain!
Here, I didn't put enough weight on the sand mold so the hydrostatic pressure of the molten aluminum separated the two parts of the sand mold and leaked everything out the side! Another costly mistakes (time-wise)
Re-hydrating the green sand after the parts were shaken out of the mold. The sand was still hot, hence the steam
Finally! The 4th or 5th try gave me a bed I found acceptable
The slab of 3/8 steel, 5" by 24" that became the bedways. I had to get it from Halifax because nobody had cold rolled steel here in Moncton
My neighbor used my cast of the bed to test his CNC router/miller machine he built.
There was a small shrink cavity in the center of the bed but since it was gonna be covered by the bedways I accepted the flaw for the sake of continuing on.
The underside of the bed
The assembled support feet, bed and bedways
A view from the bottom
Pattern for the cross slide
The cast cross slide. I had to re-do this one because the hydrostatic pressure separated the cope and the drag and spilled the aluminum out the side
Cross slide cast, machined with my neighbor's CNC machine and installed on the bedways
Pattern and sand mold of the cross slide
After the aluminum was poured
The raw casting of the cross slide which is also the base for the compound portion of the top slide
My stash of aluminum ingots I got from about 15 lawn mowers and some transmission cases. All in all about 60lbs
Pattern of the ball handle
Three ball handles cast on 1/2" bolts. Unfortunately, I couldn't hammer out the bolts so I had to melt them all up again!
Compound portion of the top slide
2 Ball handles, the compound portion of the top slide and the top slide
Compound slide ways installed
The carriage is almost done
The tool post is mounted on the top slide
Another view
And from the back
The pattern for the split nut
Nathaniel helping me shake out the casts
The apron and the lead screw bearings
The split nut with the threaded rod core still in place
The split nut, a knob, the lead screw bearings and the apron cast, cleaned up and sand blasted
Close-up of the split nut
A view from the underside of the carriage
Taking a break to figure out how to wire the switches so I can have high/low forward/reverse with the motor
I bought a 4-step pulley at Canadian Tire but since I needed a couple of them and they were each 20 bucks I figured I'd use it to make a pattern of the original and cast my own.
Filling in the back with alginate
Casting a negative imprint of the pulley with alginate
       The mold of half the pulley
Using Smooth-Cast 300, a plastic resin to create a positive pattern of half a pulley
The resin hardened in about 10-15 minutes
I cast two halves so it would be easier to create the sand mold
Adding some indexing pins to align the two halves
Here I made a single 5" pulley pattern
Creating a sand mold with the two pulley patterns
After the cast was shaken out
After the pulleys were cleaned up
Here's the cast of the split nut handle
The motor mounting base
After it was sand blasted
The assembled motor mechanism with the v-belt tightener
Another view of the motor mechanism
Here I calculated the spindle speeds with the high and low settings of the motor
Starting to make the pattern for the head stock
Drilling the head stock
The finished pattern of the head stock
Nathaniel helping me shake out the head stock
The cleaned up head stock. Unfortunately, I didn't line up the holes properly on the wood pattern so the spindle was not parallel to the bedways so I had to re-do the entire head stock pattern and make another cast. There's a bit of a hot tear but since it wouldn't affect the strength of the head stock I decided to leave it and not spend another 3 hours casting a new one
The head stock mounted on the bedways and ready for boring
Boring the head stock with a 5/8" boring bar and a temporary head stock
The adjustment template to move the boring bar cutter head in increments of 10 thousands of an inch for each pass
The bored head stock with the bronze bushings installed
Here I'm turning down one of the 5" pulleys
The rough cut and then a smoother finishing pass on the inside. The lathe was creating quite a bit of chatter and a very rough cut until I added some brass shims around the bronze bushings to tighten up the spindle. That made a huge difference and created a pristine finish
Turning down one of the three 4-step pulleys I cast. I need two of to actually run the lathe so I made one spare one to turn down and one-by-one replace the rough ones that I used to run the lathe

A cleaned up pulley. This was done before I fixed the bushings so the surface is still quite rough but at least concentric enough to run the v-belt without whobbling.
Another view of the pulley
Next on the list was to make a pattern of the face plate. This one is 3/4" thick and 7" diameter
These are patterns of the slots in the face plate. I used these to fill the rough slots in the pattern with autobody putty and make them perfectly centered and aligned at 90 degrees to each other
The patterns of a smaller ball handle, the base for the tailstock set-over ways and a reduction pulley for the automatic lead feed screw
From top left, counter-clockwise: Base for the tailstock set-over ways, face plate, ball handle for tail stock, ball handle for cross slide, pulley for automatic lead feed screw, knob for the compound slide and the reduction pulley
After the parts were cleaned up and the face plate as well as the small pulley was turned
A few iron chips from turning a 3/4" cold rolled steel spindle down to 1/2"
Aluminum chips from turning down the reduction pulley and the face plate
A before and after picture of the reduction pulley
Hand scraping the base for the set-over ways of the tail stock. I used a 9x12 surface plate I had ordered from Brunswick Industrial and some engineer's blue. After about an hour of scraping I decided to leave it and move on. It's not as perfect as I would like it to be but decided to leave it for time's sake since I have to go back to work from my 9 month parental leave in one week
The base for the set-over ways of the tailstock scraped and ready for the tailstock
Building the pattern for the tail stock
Turning the pattern for the barrel and core print of the tail stock
The back side of the tail stock pattern

The finished pattern and the imprint in the green sand mold
The finished tail stock casting cleaned up and installed
The temporary center installed in the tail stock
The finished lathe!!!

Aluminum foundry
Table saw
Drill press
Band saw
Belt sander
Bi-metal hole saws
Air nailer
Air compressor
Tap & die set
Measuring tape
Sand blaster
Alan keys
Mig welder
Bench top grinder
Bench top sander
HSS tool bits
And probably a whole bunch more that I forgot

Cutting fluid
1/2 HP motor
Angle iron
3/8" and 5/8" threaded rod
1/2", 5/8" and 3/4" cold rolled steel
3/8" by 5" cold rolled steel
1/4" by 3-1/2" cold rolled steel
Bronze bushings
And probably a whole bunch more that I forgot

About $165.00 so far

250 hrs

About $1000

It's still on-going, but so far it's worked quite nicely