Mini Molder Finished Photos!

It just occurred to me that I never put up photos of the finished Mini Molder. Here they are!

Also, if you’re wondering what’s next for the molder, wonder no more. Over the next year I plan to upgrade the machine with an automatic pellet feeder. One of the things that kept me from running the molder non-stop at Maker Faire last year was having to open the melt pot and pour in more PE wax pellets. This dropped the tank temperutre drastically and stopped the machine for a solid 45min while it got back up to temperaute .The pellet feeder will put in a little at a time, keeping the melt pot hot.

P1020993 P1020999 P1030002 P1020990 P1020985 P1030053 P1030041 P1030046 P1030028 P1030031 P1020998

Mounting DRO Scales To Your Hi Torque Mini Mill

One of the intermediary stages of my mill’s CNC conversion is mounting DRO scales to the axes. To make the stepper motor mounts I need to position the axes much more accurately than can be done by reading off the mill’s hand wheel dials. DRO’s give you good enough accuracy and repeat ability to make precision parts.

There are dozens of methods to mount DRO scales to a bench top mini mill. When designing my setup I had a few goals in mind.

  1. Minimize number of parts to be made
  2. Minimize number of holes drilled into the mill
  3. Keep everything compact and tight against the mill


For the y-axis I used the 8″ travel DRO version. Here the scale is fixed to the base and the read head follows the saddle. I mounted the scale about 1.25″ back from the front of the base using 10-32 hardware (fits nicely in the existing slots on the scale.) The cast iron base drills and taps pretty easily. I recommend a drill and tap guide be used here as matching the base’s 5° draft is tricky without one.

IMG_5701 IMG_5706

Mounting the scale directly to the base means the read head and saddle are no loner parallel. To account for this the bracket that connects the read head to the saddle has a matching 5° bend. The bracket is made from a scrap sheet of 0.090″ 5052 aluminum sheet. The distance between mounting holes is 20mm, all the others dimensions were just roughed in by hand. I clamped the bracket in a vise and use a crescent wrench and protractor to set the angle.


The holes for the read head hardware received a slight counterbore as the included screws are pretty short (with good cause, a too long screw will dig into the scale and damage it.)

A single 4-40 screw and spacer attach the bracket to the saddle. I match drilled the hole in the saddle to the hole in the bracket as this was easier than trying to measure and mark the saddle while it was in place. You’ll want to make sure you mount the rear head far enough back on the saddle that the read head does not hard stop against the scale when the saddle is all the way forward.



The procedure for the x-axis was similar to the y-axis, mount the scale, then design a bracket to mount the read head to the mill. I decided to mount the DRO scale on the rear of the table to reduce clutter near the front of the machine. Here it seemed easier to fix the read head to the saddle and let the scale travel with the table.

I started by mounting the 12″ DRO scale on the backside of the table. The scale needs to be mounted low enough that nothing sliding across the table will hit any part of the scale. Again, 10-32 hardware fixes the scale to the table.

Re-purposing the way cover mount screws kept me from needing to drill and tap into the rear of the saddle. I took some measurements of the read head position relative to the saddle, put that into CAD, and drew up a bracket.

DRO mount

A quick check of the bracket fitment in paper.



Checking for fit with a paper version proved it’s value, as one of my measurements for the way cover screw holes was off by ~1mm, if I had made the bracket in aluminum first without checking I would have had to modify the bracket I had just made.

More scrap aluminum (same .090″ 5052 as before)


Free handing the outline


IMG_5895Fitted to the read head. I needed a 2mm spacer between the bracket and the saddle. A double stack of M6 washers did the trick.


Here you can see how I was able to keep the existing way cover mount method by getting longer M6x12mm screws to replace the existing ones. The DRO bracket and spacers get sandwiched between the way cover and saddle.


For now I am just installing scales on the x and y axes. I’m going to try some work arounds to get the Z height dialed in, but I may end up putting a scale on that one too.

Building a CNC Mill Stepper Driver

When I bought my Sherline mill, it came with stepper motors, but no driver box. The drive box takes the output from a PC parallel port (small electrical signals indicating which axis should move and in what direction).

Drive boxes contain several essential parts:

  1. Power supply
  2. Stepper motor drivers
  3. Break out board
  4. Connectors
  5. Fuses and wiring

I’m kind of particular about the control electronics of a piece of equipment. Control electronics should be layout in such a way that they are easily serviced. Nothing worst than trying to trace down a problem in a rats next of wiring. Below is as list of some practices I like to use when laying out an electronics enclosure.

  1. Components should be spaced to allow airflow around them
  2. Components should be removable without taking out an inordinate amount of other components
  3. Mount components to a removable panel, rather than directly to the enclosure
  4. Wiring should be neatly bundled, using removable wiring loom where possible
  5. Removable connectors are preferred over soldered connections
  6. Wire ferrules should be used when making connections to terminal blocks.
  7. Wiring going to a removable external panel should have extra length to allow the panel to be removed without straining connections (called a service loop)

Finding the right enclosure was probably the hardest part of this project, mostly because I had many criteria.

  1. Mostly made of metal
  2. Top should be removable without taking front or rear panel off
  3. Removable front and rear panels
  4. At least 10″x10″ and ideally ~4″ tall (based on some rough dimensions of the power supply and driver)
  5. Less than $50

I found several enclosures that fit a few of the requirements, such as:

Par-metal table top series. Nice, but too much money.


Circuit Specialists EM Series Price is right, but a little too tall.

em-04-0The one I settled on was from eBay, but I also found it on amazon


This enclosure fit all my criteria. My only gripe with it would be that the front and back panel are plastic and snap in place instead of using screws.

As I mentioned above, mounting components such as drivers and power supplies to a removable panel inside the enclosure makes assembly and service much easier. Parts can be installed and wired on the bench and the panel can be placed into the enclosure in one shot. This is a pretty common practice in industrial control panels. In fact, most enclosure suppliers (like Hoffman) sell panel kits that fit into their enclosures.

I took measurements of the inside of my enclosure and cut a panel out of 0.090″ aluminum sheet. 1/4″ nylon spacers and 8-32 hardware secure the panel to the enclosure. To find the position of mounting holes, I printed out a 1:1 scale outline of the power supply and laid it down next to the driver adjusting their relative locations until I was happy with the clearance.



When it came to the rear panel layout I did use CAD software, as I wanted the connectors to spaced evenly and I needed to make sure I had room to run the wiring. Again, I printed a 1:1 scale drawing with the cutouts and screw holes marked, and traced that onto the rear panel.

controller rear controller inside

A step drill made quick work of the holes for the circular DIN connectors and AC input fuse.


The remainder of the cutouts were made on the mill.

IMG_4428 IMG_4431

A sharp utility knife squared off the corners of this cutout for the power switch on the front panel.


Skipping forward a few steps, the AC input connector and fuse has been installed and wired to the front power switch and power supply.


I used 4 wire 22 gauge shielded security system cable from McMaster to make the internal connections from the driver board to the DIN connectors. Where the wires connect to the Phoenix connectors (also called Euroblocks, those green pluggable screw terminal connectors) I terminated the wires with wire ferrules and heat shrink over the cable covering.


Using wire ferrules instead of bare stranded wire in a screw terminal is good practice, as the strands of wire tend to get broken in screw terminals, increasing the contact resistance.

If you’d like to learn more than you ever probably wanted to about wire ferrules and their use, see this white paper from Weidmuller.



A cable tie mount on the power supply neatly bundles the stepper motor cables.


One last overall shot


At this point I thought I was done. However, my decision to use the 4 axis all-in-one board was bugging me. It’s known to be buggy, and if one axis blew the board could be taken out entirely. In the name of making a more robust driver, I switched to individual axis drivers and a break out board.


The breakout board was pretty easy to mount. 4-40 self tapping screws and nylon spacers secured the board to the enclosure panel. The individual drivers where more challenging. There wasn’t enough room to lay them flat, which meant they need to be mounted on the edge of their heat sink. I thought about a few ways to mount them (screws coming up from the bottom, adhesive, pieces of all thread) before I came up with the idea of using a small strap through the heat sink fin.

Using the same 0.090″ aluminum, I machined some 3/8″x4″ straps, with 1/8″ holes for 4-40 hardware.

Laying out a hole pattern to space the drivers on a 2″ pitch.


First test fit.


Success! The driver is firmly attached, and most importantly, I can remove the driver easily if I need to change setting on the DIP switches. An added bonus is that the heat sink can conduct some of its heat away to the aluminum panel beneath it.

Fortunately the wiring I had made previously for the stepper outputs fit fine, so those did not have to be remade.


Some labels on the back finish the driver box off.



MKV GTI P0100 MAF Error Code Repair

I was driving my GTI the other day and noticed the engine was bucking/surging at low RPM. It was fairly intermittent, however the idle was smooth. The next day the check engine light went off, a quick scan of the OBD-II port revealed at P0100 code “Mass Air Flow or Volume Air Flow Sensor Circuit”. I was initially going to clean the MAF sensor, but after reading the VW forums I thought I should check the harness first.

I peeled away the split loom and sure enough there was a break in the ground (brown) and one of the DC voltage lines (yellow).

photo 2

The break occurred right where the harness makes a sharp 90 degree bend.

photo 1

I cut and soldered the wires back together (note to self: buy a cordless soldering iron). Being that this is an under hood repair it will be exposed to a good amount of moisture and needs to be sealed. Since I didn’t have any adhesive lined heat shrink on hand I covered the repair in RTV and slipped a piece of heat shrink over it before hitting it with the heat gun.

After mending the wires I also routed the harness sightly different than factory. Instead of going over the hardpipe and making a sharp bend, I ran the wire under the hardpipe allowing for a larger radius bend.


Gaggia Gelatiera Ice Cream Maker Repair

Last winter I saved an ice cream maker from going to the land fill.


This is a Gaggia Gelatiera ice cream maker from the early 80’s. While small in size, it’s a very heavy italian made machine. It’s significant weight (nearly 50lbs) is due to the built-in refrigeration system. In most ice cream makers you need to either pre-freeze a water lined bowl, or use rock salt and ice to cool the ice cream mixture. This machine uses a compressor, condenser, evaporator, and refrigerant to constantly cool the bowl. The advantage being that it is always ready to make batch after batch of ice cream.

After turning it on I soon realized why it was headed for the dump. While the bowl would cool down fine, the mechanism turning the dasher made a horrible grinding noise and wouldn’t turn. While I’m not a huge consumer of ice cream, I do enjoy a good repair challenge!

The machine was remarkably easy to take apart. About 8 Philips head screws and the top cover came off.

With the cover off, the first sign of trouble appeared: a fine black powder spread around the base.


The dasher drive motor looked okay and spun freely so it seemed the problem was coming from deeper in the machine.

Getting to the innards required removing pretty much every component from the base. To make it easier to remove all the components I disconnected all the wiring, but not before making a quick diagram.



With the base removed, the source of the grinding noise was pretty apparent.




One of the bushings on the intermediate shaft had seized and began spinning in its bore. The bore, being made of plastic, was worn into an oblong shape. This caused the intermediate shaft to become misaligned, which caused two problems. First the small metal helical gear was no longer meshing correctly with the large plastic main gear, which is why the dasher wouldn’t turn. Second, the tilted intermediate shaft caused the timing belt to rub against the main gear. You can see in the above picture where the belt cut into the gear and deposited bits of belt all over the inside case.


The new drive belt is on the right, the old one on the left. The belt wore about 1/8″ of its width off.

I ordered new parts from my favorite industrial supplier, McMaster. New bearings for the dasher drive shaft, 120XL size timing belt , and food safe grease. I couldn’t find new bushing for the intermediate shaft as they were not a standard size. I inspected the old bushings closely and there wasn’t much wear.


Using an x-acto knife I cleared out all the bits of melted plastic from the bushing bore. Fortunately there was enough of the original bore that I could get the bushing back to its original position by pushing it against the undamaged side of the bore. The damaged section was filled with 3M DP810NS, a high viscosity two-part epoxy.



The black plastic cylinder is the evaporator/bowl unit, which is connected via copper pipes to the compressor and condenser. This made for an unwieldy re-assembly. The copper pipes connecting all the parts are very small, if they become kinked they could leak, or restrict the flow of refrigerant. I found it was easier to assemble the gear train upside down and place the base on top of it.


WIth everything back together the machine was much quieter and the dasher spun properly.

No previous post-repair testing has been this delicious (vanilla custard if you’re wondering).

photo (18)


Custom Dies for the Mini Molder

Since I decided to debut the mini molder at Maker Faire bay area a custom mold was in order. One of the more iconic images for Maker Faire is the Makey robot figure. It has roughly the correct proportions for a mold-a-rama figure, and a simple enough profile for my basic CNC abilities. I found an image of a pin sold in the maker shed.

I traced the above image in solidworks and created a model of the figure.


The base on the bottom is partly for stability, but also a result of the liquid plastic entry and exit ports. Those ports are not quiet aligned with the legs of the robot, so the flat base ensures the mold cavity is always around the two liquid plastic ports.

Once the figure was modeled I created mold halves using the cavity feature in solidworks and added various holes for screws.


In most injection molding dies, water channels are used to route chilled water around the mold, this helps cool the part faster enabling a faster cycle time. Mold-a-rama dies had a water jacket cast into the back side of every mold die. The mold cylinder mounting plate on the back doubled as a block off for the water jacket.

The mold dies I designed consist of several parts:

  1. Mold face with part cavity
  2. Water channel spacer plate
  3. Rear mount plate

I decided to make the mold die in multiple parts for a few reason. The first is that more of the mold is reusable should I want to make a new mold design. If I had cut the channel for the water directly in the back of the mold, I would have to cut that same feature in the back of every new mold as well. Making a separate water channel spacer means fewer setups on the CNC mill. The second is that cutting a water jacket in the back of an aluminum mold would take an enormous amount of time on my little CNC mill, the much faster material removal rate of delrin made this an easy decision.

What follows is a mostly complete step-by-step of the machining process for the mold spacers.

After rough cutting the delrin stock and squaring the sides, it is tightened down to the tool plate in my mill.


Setting the tool height so my mill knows where the top of the stock is relative to the tip of the cutter (center drill in this case)


Drilling clearance holes for the 1/4-20 screws that hold all the mold sandwich together.

P1020537 P1020543

1/8″ 2 flute carbide end mill creating the o-ring groove.


This center u-shaped section is where the water flows into and out of the mold cooling cavity. The entire center section needs to be cut out. Since I don’t want to cut into my tool plate, I cut the slot to half-depth, then flipped the part over and cut it again. Flipping parts is always tricky, as any small misalignment will show up were the two cuts meet.

P1020557 P1020561

In the first part I made, I removed all the material bit by bit (machinists call this pocketing), this took a long time. In the second part I used a 1/4″ 2 flute carbide end mill to cut a half depth slot around the piece of delrin that was to be removed. Flipping the part over, re-cutting the same path and the whole center section comes out in one piece.


The last step on the spacer plate is to drill and tap the NPT threads for the pipe fittings. The drill bit needed to drill this hole was too long to fit in my mill, with its limited z-travel. So I milled out the hole using a 3/16″ end mill.

P1020563 P1020571 P1020576

Taping large threads like 3/8 NPT take a decent amount of torque, so your part should be firmly mounted. I sandwiched the spacer plate between two backer plates, put them in my screwless vise, and then clamped the vise to my shop table.



Getting a straight start on your tap can be pretty tough without a tap guide, or performing the operation in a mill. I used a small square to align the tap, going slowly and re-checking after each turn.


The mold faces started life as a piece of 4″x1″x12″ 6061 aluminum. Like the spacer plate before, they were cut to rough size on a band saw and then squared up with a fly cutter on my sherline mill. I don’t have as many pictures of the milling process, but I did take a time lapse video.







To remove the tooling marks left by the mill cutters, I used 400 grit wet or dry sand paper and some free labor (thanks Ashley!) It was time-consuming, but gave me a greater appreciation for what goes into achieving a mirror like finish on all the plastic products I see.


Exploded view of one of the mold dies (minus o-rings).


Spacer with its two o-rings. I used plumbers faucet grease as an o-ring lubricant as it was what I had on hand.



Assembled with pipe fittings installed.



A Pump, a Check Valve, a Problem

During testing I noticed the molder’s plastic injection pump stopped working after 2-3 consecutive pumps. If the molder sat for a few hours it would work for a few shots, but shoot blanks soon after. The path from plastic melt tank to mold goes like this:

1. The injection cylinder retracts, creating a vacuum in the pump body, which draws plastic through a check valve and into the pump body.

2. With the pump body full of molten plastic, the injection cylinder extends, building pressure inside the pump, closing the check valve and forcing the plastic through the pump outlet

3. Hot plastic travels through a copper tube to the shuttle valve, if the shuttle valve is in the plastic injection position, the plastic pass through the valve and up to the opening in the bottom of the mold.

I checked that the shuttle valve in the pump body was switching and that the injection cylinder was extending fully, both were operating correctly. The next place I could see a problem occurring was at the pump inlet and check valve.

Getting to the check valve means removing the pump body, which means draining the tank. I put a drain port on the tank, but the close proximity to the base make draining a bit of a task. A make shift funnel made from aluminum foil did the trick.


After removing the pump body from the molder I inspected the check valve and found a few particles, burnt plastic and bits of cork insulation, but nothing that would clog the inlet completely.



While I had the check valve out, I inspected the flow path through the valve. The path consisted of some very small holes (~0.050″), the molten plastic having the constancy of honey, this particular check valve could not possibly have flowed enough to recharge the pump when the piston retracted. It’s clear I didn’t consider the viscosity of the working fluid when choosing the check valve.

I looked for a check valve with the largest flow path that would fit on the 3/8″ NPT pump inlet. That happened to be a swing style check valve. The new check valve is much larger than the old one, so much so that it won’t fit in the same spot, coming directly out of the pump. A 90 degree fitting in between the pump body and the check valve put it in the upright position.


While I had the pump out, I took this opportunity to fix the threads in the pumps outlet port.



They had become cross threaded with the fitting that was installed, and was leaking when the pump pressure built up. A few turns of a 3/8 NPT tap and the threads were cleaned up.

Fast forward a few hours and the pump is installed and has a tank of liquid PE wax around it. Cycling the pump’s pneumatic cylinder it was clear the new valve was a huge improvement. You could see a steady stream of plastic flow into the check valve every time the cylinder retracted. Cycling the injection cylinder back and forth yielded a consistent flow from the shuttle valve outlet.