Bottom Up approach

[lsilva]

Hi,

As a newbie, I'll probably ask for something very common: help to decide which mill should I buy (at least for now). I am also thinking about a cnc approach.

But this time I will try to do it from a bottom up approach. I need to make very small parts from metal (brass, 6061 maybe stainless steel). As you can see in the attached picture, is a little complex. It's quite small (about 20 mm) with 2 mm holes.

So, the question is: should I buy a small mill like a Proxxon MF70 or maybe a bigger like Sherline, X2 or a Proxxon FF400. Any advice here?

Sorry for my bad english

Best regards from Brazil,

Luis Carlos Silva

[wizard]

Hi Luis;

Your english is fine! Where abouts in Brazil are you?

As to your question I thing the missing element here is: how many do you expect to produce? For a part that small just aobut all of the mentioned manual mills should be able to handle the part. If you should happen to get to making the part out of stainless you do have to be more carefull about which unit you choose.

The problem with stainless is that you have to be able to run the spindle relatively slow and maintain a stiff feed rate. That might eliminate the Proxxon and maybe the Sherline especially if you expect production quanities.

If you are serious about CNC I cannot reccomend either machine. There are a couple of reasons the first of which is the ability to easily mount ball screws on the machine. The toher reasons is that for a given investment in CNC hardware you can easily drive a larger mill for about the same cost as you can a smaller one. At least when we are talking about going from Proxxon & Sherline mills to something like an X import. That is the X1, X2 and X3 series of mills from Sieg in China.

Yes there is a certain amount of rebuilding required to get a Sieg to work correctly that you won't have with the better quality mills but once done you should have a much more capable machine CNC wise.

That is my opinion at the moment. You also need to think about future demand on the machine. I find it hard to believe that this little part lives all by itself, are you involved in the other parts of what ever this is?

Thanks
Dave

[NC Cams]

A small part like that would make a good investment casting candidate if you had to make any appreciable quantity of them.

Then again, check with a local custom jeweler. These folks do small onesy twoesy investment castings all the time with rings, pendants and the like.

17-4PH stainless would cast VERY nicely and all you'd have to do would be to ream the holes. A jeweler could offer up alternative materials for consideration....

[lsilva]

Hi,

Thanx a lot for the answers. In fact, that little part belongs to a small robot arm cardan. I will need about 10 of them, but I will also 30 pieces of another ones which are little simpler but the same size.

I am not sure about the metal I will use, I am currently trying to run some FEM simulations but my notebook is not that powerful . I was considering 6061 or brass, but I am not sure if they can handle forces envolved.

Investment cast really seems to me a good idea, since I will need to a lot of small parts, although in a near future I may build the same robot but much bigger than the actual. In this case I am really considering a CNC mill with 4 axis to help me.

Another way could be building a CNC mill from scratch. Is this a dream? I found a very good explanation on http://www.5bears.com/cnc.htm. Or retrofiting is much easier and cheaper?

Regards from Brazil,

Luis Carlos Silva

PS: I live in Brasilia, DC

[NC Cams]

Building your own machine (ala the 5bears site) requires you to have machining equipment to make the stuff. If you had the mills/lathes, you'd be beter off making the part on them. AT that point, why not retofit the machines you use to make the CNC - you're already half way there so all you have to do is fit the CNC part - the machine is already built.

Here in USA, there is a lot of imported machinery available at REAL reasonable prices. It becomes purely a matter of economics and/or accuracy needs as to which one to buy. There are also a number of ways to retrofit even the least expensive hobby lathes to do CNC work. Again, time and/or money and/or accuracy determines optimum solution for a particular application IE: make versus buy.

I'd look long and hard at investment casting. You make the mold out of aluminum and cast wax, then you "invest it" and create near net shape, beautifully detailed cast parts. Once you have the tools to make the wax part to invest, you might only have to ream the holes after casting. I've even seen cases where nicely cast parts don't even need to be machined.

Making MANY parts out of billet is espensive for EACH AND EVERY piece. Investment casting is expensive for first part but cost for subsequent parts is much less, especially if you do larger quantity and on repetitive basis.

Be realistic in your approach. You can't build EVERYTHING when making a product. If you do, you'll spend all your time making the tools and none making the parts you're trying to market in the first place....