Category: Tips

Proxxon MF70 Milling Machine

I just bought the Proxxon MF70 Milling Machine (27110), a tiny machine that can be upgraded (or bought) as a CNC machine and offers a much higher rpm than my drill press or lathe: it goes up to 20,000 rpm. I was never able to drill anything below 0.5mm without drills breaking and more or less gave up on that idea without a watchman’s lathe or equivalent, until Marijn van Gils showed his brand-new MF70 could drill almost to 0.1mm in brass (See his HMS Victory Vs Le Redoutable build). As the mill is quite affordable and I no longer have to pump all my savings in my recently completed audio project, I bought one as well.

So I did use the Drill Press with a compound table (27100), a precision machine vice (24260) and a nice dividing head (24264). But, the rate of revolutions is low and the entire setup is quite flexible and as such not precise. More important, it does not have a proper collet system but uses a large three-jaw chuck that is inherently terrible for fine work.

Imagine my surprise that the MF70 does not have a proper collet system either; it uses the Micromot collet system. That’s fine, but these cannot old larger objects such as Proxxon’s own edge finders. For my small lathe, Proxxon failed to deliver a proper collet system for the tail stock too, though that was solved by brutally cutting an MC11 ER11 collet chuck. For the mill this is not an option as the spindle doesn’t use an MC11 system, but after minor search efforts I found a replacement part at USOVO; a new tuning spindle with an ER-11 chuck and it even comes with a small installation manual. Rejoice!

I do wonder why Proxxon seem to be content with their tools not being able to use the entire range of tool mods and expansion sets among them, but at least now I could use the Edge Finder Set (24434) that doesn’t fit the original MF70 to align the vice properly and to help finding, well, edges. I did perform some tests with the Micromot collets and these did hold some of my drills perfectly centred, so I can image some people not needing the ER11 collets. I added an extra collet set in a nice box (24154, but you better buy a set with more collets for less elsewhere as this set contains only 7) plus an additional vice (the vice vice). With these options the mill became roughly twice as expensive and I forgot to buy cutters as these are not included—not even one—but small cutters can be bought as small as 0.2mm at other stores. The mill did come with a cross table (27100) and a set of step clamps (24256).

Installing the new spindle took about half an hour. I used my sturdy Gorilla-proof 1.5mm Hex wrench the remove the motor plate screws that have been tightened very well and T10 (I think) Torx driver to remove a screw holding the spindle in place. The Usovo spindle comes with two bearings but I kept the bearing of the existing spindle. The set does not come with a tool to (un) clamp the nut or hold the  ER11 spindle; I had one for the ER-11 tailstock of my lathe so don’t forget to order one if you purchase this new spindle. You may also want to order a 3.175mm ER-11 collet separately, the default size of many of my drills.

First some experiments starting with something large: a 0.2mm hole through a 0.3mm slice of a 0.7 Albion Alloys tube. Zeroing the drill position is something you’d rather do with the edge finder (that hadn’t arrived at the time of writing) and still on the very first attempt the MF70 left my drill press in the dust. The main causes for inaccuracy went into inconsistently clamping the work piece in the vice and parting the small ring using this method.

My intended targets were the davits for the 27″ whalers. This is a terribly delicate section of the model and it would be really useful if the entire assembly could be mounted by pins into the side of the superstructure when the model is more or less done. These davits are not only very thin (0.5mm rod at the centre, filed down to 0.3mm at either end plus a series of 0.7mm rings) but are also angled in slightly inward by 12 degrees. Here drilling in and soldering mounting pins and etched parts to the davit would be very useful; soldering the gripping spar to the davits would be even better as then the whaler could be glued to this spar; rope work can be added last minute. So each 12mm davit needs to be drilled in four times, two pairs of holes at perpendicular angles so the work piece needs to be rotated at least once.

With the ER11 chuck still in the mail I started with several different techniques that are all bad. I bent the davit before drilling it, worried that when bending after drilling it may break at a hole as some parts did. The drill was centred by eye (A). Bending first makes it difficult to clamp the davit so I used a block of plastic  and a small 12-degree alignment plate (B). Soldering the rings before drilling is easiest, but when traversing in steps of 0.1mm you really need to solder all these rings perfectly  if you want to hit them dead centre (C). This went well but not really something to recommend as the part will flex.  When the part needed to be rotated 90 degrees I tried two plastic blocks and re-centring the drill (D); this is awful as the part may slip (slide or rotate breaking the drill) and your reference is all over the place. Reversing the part—using a bit of rod to eyeball the angle—went better (E); not really good either with the part poorly supported. The prototype did work out nice though (the one that survived that is), after the rings from the first exercise and some etched parts where added (F). With the part flexing and overall experimentation I lost quite a few drills but it was a great introductory exercise.

Making rings with the lathe

I posted a small tip on making rings with the Punch & Die set earlier. I now use my lathe.

I use stock styrene rod from Plastruct.  I drill in the rod with the correct inner diameter and use the lathe to remove enough material for the correct outer diameter (example in the image shows this in reverse). Instead of using a parting tool, I reinsert the drill and use a knife to cut the ring from the rod; the drill with catch the ring. You can make a series of rings quite quickly and collect them on the drill. Using the knife can result in some variation of the ring thickness, but the number of rejects is a lot smaller than with the punch & die set and I can now make rings of all sizes. You do need to be careful using the knife while the lathe is rotating; this is why I position the knife as in the image—cutting with and not against the direction of rotation—so that the tip of the knife can’t be hit by the jaws of the chuck and catapult into my eye.

Cutting tubing

A small how-to on cutting steel tubing at very small sizes accurately. I bought mine from Cammett Ltd (update 2021: I switched to Albion Alloys micro-tubes that is a much nicer material to work with). The tubing comes in a wide variety of inner and outer diameters and can be most useful for small detail work.

I start cutting of a bit of tubing and inserting it into the chuck of my drill. Both Proxxon (28941) and Dremel (4486) offer these chuck as a affordable accessory to their drills next to their range of collets. At this point I usually sand down the tube. I then use the depth probe of my caliper to insert the tube into the chuck with the to-be-cut tubing sticking out at the right distance. The drill is switched on and I use a sharp knife to cut off the tubing in a sawing movement. I do this carefully, as the part sometimes jettisons away. Don’t try to hold the part in place using a finger, you might inadvertently drill yourself. After the tube is cut, I use a precision reamer to clean the remaining tubing. I do this by hand, I lost a few reamers with the drill turned on. Positioning the reamer is probably the hardest part.

Now the small tube needs to be cleaned, but it can be very small and near-impossible to hold. I use the reamer to pick up the tube and reinsert into the chuck. I apply the reamer when the tube is again firmly in place and a drill to check if the outer diameter is larger enough after cleaning (and for drilling). Sanding down the part at this point is also possible. At the end you have small pieces of tiny tubing at a consistent size. Using the macro setting of my camera shows the edged are a bit rough, but it’s a 0.5 by 0.5 mm part.

Making rings with a Punch & Die set, part II

I posted a small tip how to make rings with the punch and die set (here). I made a small refinement that allows for the punching out of holes from rod or disks. For this, I used the Waldron Sub Miniature Punch & Die set (any set will do). I would advice people who want to do scratchbuilding to buy both Waldron sets (or make their own).

1) Take a styrene strip with a hole so that it can swivel around the pin of the set. The strip should be as thin as or thinner than the working material.
2) Place the strip in the set and punch out three holes. One hole is for the working disk, the other two for positioning. Do not remove the punches until all three have been used.
3) We now have a simple template that can be repositioned using the two outer punch holes.
4) Now, drill the center hole to the exact diameter of the working material. I also added to holes at the far ends of the strip and added two disks with the same height as the disk.

5) Insert the disk into the center hole and press it so that it positioned tightly.
6) Position the styrene strip and fix it using  the outer punches for the exact location
7) Gently punch out the center of the disk and remove all punches. Swivel the strip outwards and remove the ring.
8) Make many!

The advantage of this technique is that it works for all combinations of inner (depending on the punch & die set) and outer diameters. You only need to have the exact drill size ready, which is much easier than making sub punches on a lathe as with my previous tip.

Update added 18-01-09

A small refinement was added to this tip. I let the styrene strip swivel around the largest punch. The second punch is taken to set the strip into position with the third punch for the actual punching. The pic shows I use an array of holes. Top left shows the positioning with the smallest punch. At top right the holes are drilled in where the rings can be positioned. Bottom left shows a series of 10 disks in place with the result shown at bottom right. From the close-up is visible that not all rings are concentrically, so you need to throw away some of them. I also marked which side of the mould is up, as reversing it results in all rings being punched off-center.

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