Choosing the right path. New or Used? Prebuilt or Retrofit CNC?

[w0067814]

All,

Like many people here, I am looking to start machining as a hobby. I am an electronics engineer by profession, so I am happy with the electronics and control side of CNC, and I have a practical experience in metal working from my college days, though that was about 8 years ago. (manually controlled Boxford STS 10.20 lathes and Bridgeport Turret Milling machine for the most part, but we did have access to a small CNC mill, general metal work, and welding.)

I also have a friend who owns a professional machine shop who I have spoken to about getting into CNC machining as a hobby, though there is obviously quite a difference in the type of work that he does, and the amount of monitory investment (eg cheap second hand machine for him would be £10k - £20k).

I am planning on making precision parts for gas turbines to support my model helicopter interest. I also plan to make parts for other engines such as stirling engines and small IC engines. I would like to be able to hold a tolerance of 50um (~0.002") as a maximum. I expect to be machining aluminium for the most part, but I would also like to be able to machine mild steel and some of the more exotic materials that gas turbines require such as inconel alloys. I would estimate that 200mm would be the largest diameter that I would want to turn on a lathe, and 200mm x 400mm on the mill.

I shall need to purchase both a lathe and a milling machine, both of which will require CNC control.

I have a single width garage that I shall turn into my workshop, so this is a fixed size constraint on the machines. (roughly 7'6" wide by 18' long, by 6' high). It has a level concrete floor and concrete block walls. There is single phase 230v mains electricity.

I am reading around the subject and many forums in an attempt to come to a conclusion on which type of machines are best suited for my needs. I have not yet fixed a budget, but a good place to start would be £1,500 (inc VAT) per machine (to include the motors if retrofitting CNC), though the controller PC and the stepper / servo drives are excluded from this cost as they can be shared amongst machines with a little thought as I shall never use two together.

For computer software, I have access to OneCNC, Solidworks 2005, and I could purchase something if required. I am considering using the Linux EMC motion control software (http://www.linuxcnc.org)

I know that some of the questions below are a little open ended, but I am just trying to get a feel for things at the moment, so I will ask more specific questions in due course. I do not intend for buy for at least 6 months, as I have a house to finish first. :-(


---

1.
Reading around the forum there seem to be many people who are using Chinese imported machines, and they appear to have very poor accuracy out of the box and require quite a bit of massaging to get a decent performance out of them. On the plus side they are very competitive on price and are readily available. I wonder what are the relative merits of buying a machine such as this new when compared to buying a second hand industrial machine and retrofitting CNC controls? Would I ultimately end up with a better machine if I were to buy a heavy old (semi) industrial machine (perhaps even the Boxfords that I used to use) for circa £1,000 and spend £500 on motors and retrofitting than if I were to buy a pre-built new imported machine for £1,500? I think that I would be less likely to out-grow a larger retrofitted machine than a new small bench top.

2.
What are the pitfalls when retrofitting old machines? Are there any machines were the complexity and cost of the retrofit make it not worth while? Are there any old machines that are particularly worth my while looking out for, or avoiding given my tolerance requirements above?

3.
If I were to go down the mini-mill / lathe type of route, I have been looking at the Wabeco offerings. Has anyone got experience with these machines and care to comment? They seem very rare second hand, so I presume that people are happy with them are are holding on to them. What is the second hand price range for these machines?

4.
If I were to go down the retrofitting route, what am I likely to need to do in order to make the machine function as I need other than replacing the manual handles with motors and mounts? (ignoring PC software, Drives and controls) What are typical areas that require attention or close inspection on second hand mills and lathes?

5.
What would be the likely torque ranges that would be required of the motors to retrofit machines (given that the motor cost is generally proportional to torque), and how could I go about estimating them for a given machine?

Regards,

Tim Warren

[NC Cams]

IT all comes down to time and money - how much do you want to spend and what are your REAL goals and REAl compromises??? The answers to these questions are the first things you need to pin point and this will help you decide what's best to buy.

You have a choice of buying equipment and MAKING parts for your hobby or else starting a bunch of science projects so as to build the machines that you want to get that will make your parts. Which is more imprortant/ Making parts or creating the science project???

I took the project route toward structuring my business. It worked but took way more time than I cared for it to do so. It cost me a LOT of business as i was not timely in my deliveries - I simplely did not look nor act professionally which is not a good idea. Even so, I persisted and kept moving the ball forward.

We have the precision we'd hope for. We're still hunting and pecking for more business. The business I do get is profitable and my clients are satisfied. And the equipment is the most expensive that I can hardly afford. If I had it to do over, I'd DEFINITELY spend more money and buy better equipment - you waste too much time and money screwing with lame hardware when trying to concudt business. However, if it is a hobby, a REAL hobby, that's different.

The key is to be REALLY honest as to what your'e trying to do/achieve. Is this a subterfuge for a secret desire to be self employed or is this REALLY a hobbby. Treat the afliction with the proper care and feeding and it will manifest itself quite nicely.

[w0067814]

This is for hobby use only. No time constraints. No cash income.

Short of adding stepper motors and possibly encoders to a machine I am not interested in building anything for the machine. I need decent accuracy, and as I have yet to setup a workshop, making a machine woudl be difficult.

I was asking about the merits of buying a _NEW_ prebuilt CNC machine against retrofitting steppers to make a _SECOND HAND_ manual machine CNC capable. Would I end up with a better machine this way (for the given budget), or is it likely to be more hassle than it's worth?

As stated the target budget for either method is £1,500 (UK pounds stirling) per machine (ie to spend a total of £3,000 on both a lathe and a mill) .

Thanks

Tim