Seeking high-precision milling machine for mild steel, better than Proxxon MF70(!)

[LKeithR]

Talk to Dan Gelbart. I'm sure he could make you something...

https://www.youtube.com/watch?v=sFrVdoOhu1Q

[RB211]

I am beginning to understand why they are the way they are over at Practical Machinist.

[small.planes]

Small planes, what was the bigger advantage of the new head that made the difference? I can see two things being an issue. First is for small carbide cutters any play or vibration in the bearings at all would be disastrous. And second would be any but the most microscopic of runout in holding the tiny tooling.

Mostly it was runout. The new spindle is ER16 direct with about 1/10 of the runout of the Proxxon one.
The Proxxon head is also limited in its max holding diameter and the free length you can stuff inside to reduce the stick out.
With the new head I can run 6mm shank tooling stuffed right into the collet.
The Proxxon also has a tiny brushed motor which is not ideal for longish runtimes - its noisy and You can hear it slowdown on cuts...

[elf]

Perfect: https://pocketnc.com/products/pocket...11607895998511

[Paul Alciatore]

Point by point in red within the quote:

Nope my question was serious.

Thanks for all your replies & suggestion folks. I shall go through them in detail properly when I have time.

My central point is tha tthe Proxxon MF 70 weights just 7Kg (15lbs), and goes up to 20,000 rpm (faster than I need). Its motor rather weak though at just 100watts, and whilst an over-priced brand, and although it is quite well made in some ways there are lots of hideous weaknesses - Proxxon just never quite finished doing a decent job of it. Even the spindle is said to be off true by 0.003inches.

All motors will have design compromises. Weight, size, power/torque, power consumption, efficiency, and of course cost. A happy thing here is that most motors have a standard mounting interface so you can buy and use one you select with more of your design choices. But you will not be able to find everything you want in one motor. You certainly can find a motor with greater HP and high speed but expect to spend $$$ for it unless you can find it from a surplus seller.

But what I don't understand is why, with gearing, you can't get a properly powerful motor (e.g. 750+ watts) to go essentially any speed you like? It's called a gearbox. They work well on things like cars/automobiles. Or probably more durable in the event of sudden stops would be pulleys somewhere in the power chain.

A gear box that would allow the speed range (600 to 10K RPM) that you want would need a 16.66 to 1 range. Fortunately, the motor's speed would likely be in the middle of this range so you would be gearing both up and down. With 60 Hz power a common motor speed is about 1750 RPM (about 1460 with 50 Hz). So a reasonable assumption would be a step up of 5.7X (6.9X / 50 Hz) and a step down of 2.4X (2.9X / 50Hz). A 3000 RPM motor would change these numbers but either way this would be possible with a single stage gear box. A single stage gear box would be desirable to avoid friction losses which would become larger with additional stages. But it will have both a cost and WEIGHT. It could easily cost and weigh as much as the rest of the milling machine without the motor. Few manufacturers will be willing to make such a design without a strong market for it.

You mention pulleys. My Unimat DB200 has pulleys. The stock Unimat has pulleys with three levels and one intermediate one. This allows a range of speeds from about 900 to 7500 RPM. I have the Slow Speed accessory which adds a second intermediate pulley and extends the speed range to about 300 RPM on the low side to some unknown value (they do not state it and I have not measured) on the high end. The problem with this is that this additional pulley stage also comes with additional friction and power loss. I only use the slowest speeds when absolutely necessary and have never even tried the ones higher than 7500 RPM.

A two speed motor or one with a variable speed control may be nice here. But those will require controls which also add weight and cost. I am not a big fan of variable speed motors for obtaining lower speed operation. The reason for this is that speed controls generally do not increase the torque at those lower speeds and more torque is exactly what you need when running a lathe at lower speeds because more torque is needed for turning larger diameters.

All of the above means that the speed ranges that most OEMs choose for their lathes are, more or less, the optimal ones for that size machine. The bed and frame size determines the useful motor power. Then that motor power determines the useful speed range and work envelope. All of those factors are inter-related and yes, there are compromises, but those compromises have limits.

Look, even my bosch hand-held hammer drill is 750 watts, and it only cost about GBP 65.00 and it does 3000 rpm, WITHOUT any gear or pulleys. Why are all these mills so under-powered? I know it's basically just a motor but it's light too - only about 1.5 Kg.

Remember I was speaking about design compromises. A big part of the reason why your hammer drill runs at that speed is because it does not have any pulleys or gears. That design choice lowers the cost and decreases the weight. That 3000 RPM is about two times the 1460 RPM figure I mentioned above for 50 Hz areas and is a design choice in the number of poles and how the motor is wound. I am not familiar with motor speeds in 50 Hz areas so the 3000 RPM number may be more common and less expensive than the 1460 RPM figure I used above. But basically your hammer drill is simply a low cost design and the 3000 RPM number comes from that design choice (low cost). A hammer drill or any other hand held tool that runs at your 600 RPM speed will require gears or pulleys and will cost more and weigh more.

I'm obviously missing something, but what?

What you are missing is the totality of what has been said here.

PS I am new to all this, and obviously I don't know what the heck I'm talking about, but all the machines that I've seen don't look like the've had a facelift or a redesign since the 1950s!
Look, I don't want to be rude nor inflammatory... but to some extent do I have a point?!
Seriously if I am to spend say GBP500 to 1000... has any of this technology significantly improved since the last century?!

Your GBP 500 to 1000 translates to US$ 700 to 1400. That is the price range of LOW END milling machines. So is your desired weight. Yes better machines are made. But they WILL BOTH cost more and weigh more. For a milling machine, "better" starts with a heavier (therefore more expensive) base/frame. All the larger parts MUST be beefed up to have a "better" milling machine. And that is just the starting point.

One "better" technology that is used on high end mills and other machine tools is precision ways with linear bearings and ball bearing feed screws. But these items cost a lot more than ways machined in cast iron and Acme lead screws. And those "better" ways still need to be supported by heavy, cast iron pieces under them. There are other "better" technologies that are used in modern milling machines and I can guarantee that all of them cost more and most of them will add weight. Your price range a.most completely eliminates most of them.

You will almost certainly need to make some compromises in your wish list. One possible one would be to look for a used machine and be prepared to make the needed repairs on it. I sincerely wish you good luck with this.

[RB211]

It's like asking a Cessna 172 to provide lift across the Pacific Ocean. The excuse being a 777 won't fit in the hangar.

[elf]

I think you should stop thinking mill and start thinking CNC router. Stefan Gotteswinter likes this one.

[JoeLee]

I had no idea what a Proxxon mill was until I found a picture. It's a toy ! Who considers .5mm to be precision milling?? I can do better than that with my X Y table and drill press.


JL..............

[JohnMartin]

I am beginning to understand why they are the way they are over at Practical Machinist.

I was considering suggesting that he ask over there, but thought that all here might not understand. You summed it up nicely.

[Bented]

This is almost the machine required but lacks the lowest spindle speed and the accuracy.

https://pocketnc.com/collections/pocket-nc-v2-50/products/pocket-nc-v2-50?variant=11701775040559

[ikdor]

You could also look at the Roland desktop cnc machines but they will not fit the budget either.

[reggie_obe]

If you can relax one or two of your requirement. You might find find a machine meeting most of the other ones.
Maybe you can co-op your neighbors garden shed for space so you don't need a hand-carry machine?

[ship69]

I am away now for the weekend, so I won't have time to nvestigate everyone's suggestions in detail, but here are some quick thoughts & responses:


@thin-woodsman

I am new to mills and know nothing about this subject but I simply don't get this line of argument.

Rather than twisting the entire mill out of shape, why can't they build in a torque-limiting connector (or whatever the correct engineeering term is)? Maybe build in a amber flashing warning light when torque is approaching the limit and a red light light once it starts to actually slip.

Also by keeping the whole machine fairly compact, the distances small the leverage forces would be smaller.


@Rich
I had thought that CNC would be A) more expsensive than a manual machine, plus B) there would be rather tedious long learing curve, and depending on the sophistication of modern CNC software I might end up destroying the whole machine during my learning phase.

But in the end I just want the cutting to be acheived, so maybe I should I should think again about buying a smaller CNC machine and let it take its time to cut stuff out.

I don't really believe that no one has my needs. My needs are pretty pedestrian. I just want to do some milling at a fine scale on stainless & mild steel. But if I am to spend many hundreds of GBP, then I may as well get something that can work on something larger than the very small cuts (1mm?) that the Proxxon MF70 is capable of.

Either way at just 7Kg, the MF70 is actually MUCH lighter than necessary, and at just 100watts its motor seems rather pathetically weak. And from the reviews the build quality isn't great either. But it DOES show what is possible!

10,000 RPM would do me, I don't need to go up to the 20,000rpm that the Proxxon MF70 can do. If the 7Kg Proxxon can do 20,000rpm, why can't he have a 30Kg mill than can do 10,000rpm?

Yes, I have been compelled to outsource jobs but that means slow turnaround times (e.g. 1 to 2 weeks and huge expense typically GBP 100+ per job.


junkaddict - sure the frame may flex bit when cutting mild steel, but if I want precision surely I can just finish off doing very fine cuts.


@small.planes
> MF70 based, 750W spindle, upto 24k rpm.
Just to get clear is this something that you have built?
If so that DOES sound interesting. That photo is rather tiny on my computer. I like the look of that enclosure - although I would need to take it down every night. Where did you buy the 750W 24k RPM spindle from? Do you have problems bending the mill out of shape - or have you got some sort of torque limiter in place?

Either way, I am new to all this do I would much rather buy something off-the-shelf than dive into the deep end re-inventing the engineering... IF something like what you seem to have built is available off the shelf (?!)


BCRider - there is of course the MICRO miller FF 230 (for x2.5 the cost for the MF70) but its top speed is only 2,200rpm so I doubt it would work well on fine diameter cuttting.

Yes, am based in Europe (the UK), and I would need METRIC scales

Realistically what is the largest diametre (side cut & end cutting) that you can cut into mild steel on your heavily modified MF70?

hoof - from what I can see the Aciera F1 weigh 120Kg.

https://www.db-machines.com/en/produit/aciera-f1/

That is 4 times the maximum weight of what I am looking for!


elf - I can't really work out what a Pocket NC V2-10 is, nor how you would use it. But at least it can do 10,000rpm. Sadly it is unable to do slowing than 2,000 RPM. Either way I think it is outside my budget (did I see over $5000?). My budget is upto £750, mabye £1000 but that would be for something really exceptional.


paul Alcitore - I hear you but what I am looking for is VERY close to the Proxxon MF70 - which already exists! I just want something that is
A) Slightly SLOWER RPM (max speed 10K not 20K)
B) Quite a lot heavier (weight 30Kg not 7Kg)
C) More expensive (upto say GBP 800 not GBP 310)
D) Hopefully a bit more power than 100watts
E) Rather better made

...How hard can this possibly be? Why does everyone keep saying my requirement are totally impossible, if they are so close to the Proxxon MF70(!)

J

PS Maybe I'll just buy a damned Proxxon MF70 and be damned. I just feel in my bones that it must be possible to do better than that, particularly if I offer tripple the money! What am I missing?


PPS My apologies that this is a slightly rushed reply. I shall investigate your suggestions properly when I have more time next week.

[strokersix]

To OP: Perhaps if you post specific examples of what you intend to accomplish (parts you want to make) you would get more specific advice on how to accomplish.

Or put another way, how did you arrive at your specification list? With your admitted lack of experience, I doubt you really understand what you are asking for.

I don't mean to be condescending. Sorry if it comes across that way.

[Brian H.]

The only machines I know of that would in fact fulfill the stated requirements in a (nearly) out-of-the-box state would be the Sherline and Taig mills.

OP's requirements:

1. Good build quality designed for milling. With regard to the Sherline, to say the least it isn't the largest or most rigid of all milling machines, but it *does* serve the purpose (and it's a whole heck of a lot more capable than the Proxxon!). Sherline is generally known for good fit and finish, and their machines are relatively accurate for what they are. The Sherline mill is able to hold tolerances of +/- .001" (.02mm) if the operator does their part. The Taig mills are a bit more substantial (better geometry, steel construction on the Taig vs. aluminium on the Sherline) and probably a bit more accurate (ground square-section/dovetail ways on the Taig vs. precision-milled dovetail ways on the Sherline), so in this regard I'd say the Taig is the better machine.

2. 600-10,000 RPM spindle speed range. The Sherline will do this with the substitution of a 10,000 RPM pulley set, which is available as a standard accessory. To be honest, the standard 70-2800 RPM pulley set works well for most general operations. If you frequently run tiny cutters or engraving tools, though, the 10K pulley would probably be worthwhile. Taig states that their standard RPM range is 525-5200 RPM using a 6-speed step pulley; they also state that their CNC-ready (CR) and CNC mills have a modified speed range of 1,000-10,000 RPM, again using a 6-speed pulley setup. I'm not sure if this is due to a different pulley set or a different speed on the "upgraded" motor.

3. Weight < 30 kg. Sherline's website states 18 kg; the Taig mill is 36 kg. This puts the Taig over the preferred 30 kg, but it's still less than 50.

4. Motor > ~150 watts. The Sherline motor is a 90-volt variable speed DC motor that does around 300 watts, and is compatible with 50/60 Hz, 110-240V input, requiring only a different cord (or an adapter). Taig's "upgraded" motor is an AC induction motor that's only 180 watts, and has 6 fixed speeds; they do not state whether it's a dual voltage motor. To my understanding, modifying the Taig mill to use the Sherline motor was at one time somewhat popular. The Taig does maintain its full power at its lowest speed, however, whereas the Sherline motor does not. The Sherline does have a two-speed pulley to help its low-end spindle torque.

5. CNC upgrade capability. Sherline offers CNC upgrade kits in a variety of forms, from simple "CNC ready" kits you can attach your own motors and drives to, to full kits that include a computer. Taig's website doesn't appear to list upgrade kits, only CNC-ready and prebuilt CNC machines.

6. Milling capacity up to ~5mm end mills. The Sherline will run a 1/4" (6.35mm) end mill 1/4" deep in 303 stainless steel, though that's really the limit of the machine with a stout setup. The Taig's construction will allow it to do a bit more - on either machine, use roughing end mills if at all possible. In general, the smaller the machine, the less material that can be removed in a given period of time. If you want to go faster you will need to find a larger and much heavier (and more expensive) machine.

7. Metric leadscrews/handwheel markings. Sherline offers all of their machines in both inch and metric versions; Taig, as far as I can tell, is inch only.

8. Price < ~1000 GBP. Both the Sherline and Taig machines are not inexpensive. Tabletop machine tools are a niche market, much more so than hammer drills that are sold in quantities of millions. I'm assuming the OP is in the UK, so these machines are likely to be more rare there than in the US. Ergo, finding a used one might be difficult. It looks like a new Sherline 5410, which has metric screws and handwheel markings, would run $825 / 600 GBP (at today's exchange rate of $1.38 / 1 GBP) + shipping. The Taig lineup starts at $960 / 700 GBP for the 2018ER mill with the upgraded motor. One also needs to budget for accessories, though; for $1,102 / 800 GBP the Sherline can be purchased with an accessory kit that includes a drill chuck, mill vise, collets, strap clamps, and some end mills. Taig does not appear to offer accessory kits, only individual items. There are also some common accessories that one might wish to purchase with a new machine (boring head, rotary table, etc.) that should be budgeted for if desired.

So there you have it. Honestly, I feel that the Taig mills are probably a more useful machine overall in that general size range due to their extra weight and more rigid construction, but they're substantially heavier, have a relatively small motor, and only a modest range of accessories. Sherline offers a much more extensive range of accessories compared to Taig, and (in my personal opinion) a much better motor setup. Finally, Sherline's customer service is excellent; I have not dealt with Taig and so cannot offer any useful comments in that regard.

To the OP - There are certainly "better" machines available - but as many others have noted, you'll be looking at larger, heavier, and more costly equipment to gain more power, rigidity, and capacity. Do your own research, and understand that there is no one "perfect" machine. It comes down to what you feel fits your needs best, and you are the best one to determine that.