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View Full Version : Proxxon MF70 for making injection molds



forrest
31-01-2011, 08:42 AM
Hi All,

Hope this is in the correct place, in the not too near future I hope to buy mini CNC mill of some sort to make some injection molds, these wont be for anything big just a benchtop unit,

My question is will the MF70 give me enough accuracy/strong enough, I dont mind the slow cutting speed (for now!) and small cutting volume,

All the stuff I have seen so far on youtube etc has been of these machines cutting plastic or wood. Some aluminium but that was just drilling a few holes,

I wont be using a hard ally just bog standard stuff,

any views welcome

John

AdieR
01-02-2011, 03:48 AM
What size moulds are you looking to do? What tolerances (deviation from given size) are you allowing? What accuracy are you expecting?

Beware, aluminium can be a PITA to get a decent finish on, especially if you haven't done it before (esp if you try running high speeds / feeds, or take big cuts).

If you're doing ali, keep some paraffin as a coolant.

forrest
01-02-2011, 08:47 AM
Good questions :) The overall mould size would be 50x50x50mm approx so two halves of 25x50x50mm. The actual part size to be moulded initially is only 8x8x15mm. As for tolerance I guess I would be looking at a minimum of 0.1mm,

It would be intesting to see what results other people have had from a proxxon as it looks like the ideal machine to start to learn about cnc machining

I could ask my dad to hand mill the overall mould dimensions then use a proxxon to do all the intricate work, or my other thought was to machine the mould out of brass which would machine better but might not be as good for the injection moulding bit,

I might just buy an normal proxxon to get used to it(see if it might be capable of doing what I want), then cnc convert it, at the moment whilst a self build looks tempting I neither have the time or experience to build such a beast.

The bench top injection moulder I have is a Small power machine co SP2 with an air operated piston, my other possible plan is to cast a mould with aluminium powder loaded epoxy resin, but whilst I have heard people talk of doing this on the net I havent seen any results yet,

Jonathan
01-02-2011, 02:52 PM
I could ask my dad to hand mill the overall mould dimensions then use a proxxon to do all the intricate work, or my other thought was to machine the mould out of brass which would machine better but might not be as good for the injection moulding bit,

I think that could be a good way of doing it. The main problem might be finding a CAM program that can generate toolpaths from a partially machined item. If your dad can get it close enough that the whole thing can be machined on one or two passes then it could be efficient. If there's too much material left then you've got to work out where it is and add roughing operations to remove it - doable even with a simple program like cambam, but tedious if you have a lot to make.

Brass can be much quicker to maine (SMM is very high), however you're limited by spindle speed and the cutting force...


Beware, aluminium can be a PITA to get a decent finish on, especially if you haven't done it before (esp if you try running high speeds / feeds, or take big cuts).
If you're doing ali, keep some paraffin as a coolant.

And equally if you feed it too slowly the cutter may rub and leave a poor finish.
I think paraffin could be bad for the machine, having such low viscosity means it's going to get into everything.

M250cnc
01-02-2011, 03:26 PM
I will add that it appears that the tables are made from ali so it ain't gonna last long.

As Jonathan mentioned to do 3d , cam software is expensive.

When doing 3D the software i use is able to rough out using large cutters then doing REST machinning using smaller cutters to get efficient toolpaths.

On a shape i programmed which was in your work envelope the machining time was in the order of 18 hrs this was using a roughing toolpath so even longer using a single smaller cutter.

Good Cam software can cost 3K +

Phil

AdieR
02-02-2011, 02:21 AM
"I think paraffin could be bad for the machine, having such low viscosity means it's going to get into everything."

Paraffin is no worse than standard water-based coolants in this regard.

What I have done before today is to put some paraffin in a bottle (500ml Coca Cola bottle or similar), with a small hole punched in the top, and squirted it when and where I wanted it, that way you don't have a huge amount of mess to clean up (Just make sure you identify what's in the bottle so it doesn't get mixed up...)

Not sure I'd be using brass for Injection moulding though, I'm not convinced it would work.

What temperature you anticipate running your moulding machine at?

forrest
02-02-2011, 09:05 PM
Thankyou all for the informative replies, I never for a minute thought this would be easy, Adie R the temperature range is 100 - 300C depending on the type of plastic and size of mould, so that is comfortable under the brass melting point,

One other question aprroaching it from a slightly different angle, does anyone on here have a proxxon (or similar) and what have they managed to achive with it. I am guessing it is essentially a Dremel type motor/chuch bolted to a xyz table stand?

Rabies
03-02-2011, 06:05 PM
I have an MF70 that I converted to CNC a few years back. It's a neat little machine, but to be honest it's not as much use as one would hope. Reasons below.

Starting with the good and working downwards: it's a well-enough built machine. To compare it to a Dremel is a little unfair -- the head is cast aluminium with good bearings and no play in the spindle -- but in terms of scale, it's much the same (although it has a metric spindle nose of Proxxon's own devising, so Dremel collets, chucks etc. won't fit.) The base and the saddle are chunky castings too, giving the whole thing some degree of rigidity. The column is an aluminium extrusion which isn't terribly rigid but good enough for the small forces needed to take small cuts in light materials. The 150w spindle motor is reasonably sized for the machine, but has a habit of letting the smoke out if it's allowed to stall.

The table is another flimsy extrusion which bends as you attempt to clamp anything to it, affecting the fit in the saddle (as you tighten a clamp bolt, the table edges pull inwards and take you from a snug fit to a wobbly one.)

On to operation: It will cut aluminium perfectly well, but makes a hell of a noise while doing so, and you can only get away with very light cuts (1mm width/depth of cut is reasonable, much more than that and it will seriously struggle.) If you try to make it bite off more than it can chew, you will either stall the motor, or get terrible chatter and a poor finish as the column/table flex around too much. The spindle will only hold tools up to 1/8"; if you were to jerry rig anything bigger in the motor probably wouldn't cope with it anyway, and machine rigidity would be even more of a problem. The actual working envelope of the machine is pretty small but that's just as well because it would take forever to machine anything larger than a couple of inches on each side.

Overall opinion: the machine is well made and (unlike many Chinese machines) doesn't need tweaking to make it work, but its working capacity is too small to be useful for very much. It will work aluminium (to prove this point, mine was used to make its own parts for the CNC retrofit), but you have to take it very very slowly, and be prepared to put up with a lot of high-pitched noise. Much better value for money would be something like the Sieg X1, which (despite forgoing warning about Chinese machines) is a much more capable little mill.

Just my opinion, of course.

Richard

Colin Eldon
12-04-2012, 12:30 AM
Hello from California.

I was a field salesman for The Small Power Machine Co from 1971 until 1976 and traveled the UK with an SP1 and an SP2 in the trunk. Richard Benson and Pete Glasson ran it, Ian Berg was the Sales Manager, John Few ran the molding shop and me and Dave Hiscock ran around doing the selling. Boy, have I got some stories to tell. The worst was blowing up the machine - split the barrel, heater bands became shrapnel and the guards shattered. It was at The Royal Ordinance Factory in Bridgewater trying to mold a tensile test bar outa solid rocket fuel. They assured me it was inert and just the matrix with no explosive.....WRONG. Ian Bergs sympathetic reply to me shaking on the phone was "That's sales for you". I named the last machine they made "The Hotshot". I would love to get a picture of an SP2 and in particular the optional Ejector Unit.

Cheers Colin Eldon
celdon44@gmail.com


Good questions :) The overall mould size would be 50x50x50mm approx so two halves of 25x50x50mm. The actual part size to be moulded initially is only 8x8x15mm. As for tolerance I guess I would be looking at a minimum of 0.1mm,

It would be intesting to see what results other people have had from a proxxon as it looks like the ideal machine to start to learn about cnc machining

I could ask my dad to hand mill the overall mould dimensions then use a proxxon to do all the intricate work, or my other thought was to machine the mould out of brass which would machine better but might not be as good for the injection moulding bit,

I might just buy an normal proxxon to get used to it(see if it might be capable of doing what I want), then cnc convert it, at the moment whilst a self build looks tempting I neither have the time or experience to build such a beast.

The bench top injection moulder I have is a Small power machine co SP2 with an air operated piston, my other possible plan is to cast a mould with aluminium powder loaded epoxy resin, but whilst I have heard people talk of doing this on the net I havent seen any results yet,