Paul,

Some things to consider:

The cost of moving and installing these big machines matches their

weight.

The large machines are so difficult and expensive to deal with that

they

wind up going for scrap, or lately loaded on a boat to China. I wish I

was

kidding. Plus if anything breaks you will be on the phone to guys who

ask

for your credit card number and bill you at $100 an hour to tell you

it will

cost $5000 or more to fix the problem. There is a reason that large

machines

are cheaper than the small to medium machines, sometimes free if you

will

just come and get it. Price the tooling also. Price some cat 40 and 50
tooling and tools. Do you have enough juice to power a 10 horse 3

phase

motor at your hangar?? Priced installing a load center to do that

lately?

How about the slab, is it just a measly 4 inch slab or the required
thickness for that weight? I had the same Idea to put a machining

center at

a hangar at my local municipal field. They had a big drive to

re-develop the

airport. The rent was cheap. The code situation in Arkansas is

ummmm.....

"liberal" but it still was going to cost me a fortune just to install

my

little mill. I can't imagine dealing with the code Nazi's in Kaliforia

on

such an issue. Before it was over, I was going to have to spend 10K

just to

get the services installed.

I have seen some small bed mills go for very reasonable prices lately.

If

you are going to get a machine I suggest looking into this. I probably

will

get one as soon as my shop is finished. Some things that are nice to

have is

and enclosure, coolant system, and tool changer. It is pretty easy to

check

a machine out once you know what to look for. Always try to get one

that is

under power so you can check it out. You can also usually tell if the
machine has been abused by it's general appearance. There are a lot of

used

tooling dealers on the west coast with a lot of inventory right now.
Unfortunately I can't recommend any of them because it is too far from

me

for shipping, so I haven't dealt with any of them. Surely there is a
reputable one out there that will guarantee a machine being good. Just

do

some asking around. Crooks tend not to stay in business during lean

times.

Monty

OK Monty I hear you I have three phase 220 but I don't think it will
handle 10 HP. Also my slab may not take it. What is your guess on the

weight

of the Mazak?

Paul Lamar

A couple of more questions if you don't mind. Can I use the DRO sensors if

I

convert a Chinese mill to stepper motor NC? I note that Enco is having a

sale

on a 9 x 42  knee mill with DRO and table drive for $3,995. free shipping.


Is it usable? I can save $1600 if I don't get the DRO and the table drive.


Should I do that and install a NC retrofit?


Will I have to change the screw drive to a ball screw drive?


If so what will that cost?

Thanks Monty.

Paul Lamar

Paul,

I would recommend against trying to retrofit one of the Chinese mills. To do
any meaningful work you would have to install ball screws and they would not
be cheap. You could easily have $3K in just steppers and ball screws on the
low end. You could possibly use acme screw and a double nut to take out the
slack, but it would wear and have a lot of drag. It really is not a viable
option. That is the wonderful thing about the Bridgeport Boss Mills, they
already have the steppers and the ball screws. Everything is heavy duty. The
castings are really high quality, unlike most of the Chinese stuff. There
really is no comparison. Hardened chromed ways are standard. All you do is
hook up the new electronics and go. No brackets to build or ball screws to
install. There is also the added benefit of all English standard bearings
and belts which can be bought at your local bearing house (much less
expensive than Bridgeport prices).

There really is no comparison between the machines. They come with auto
lube, most of them have mist coolant systems already installed. I have seen
one machine that was in a trade school that looked like it had never been
used go for $1200. Everything was still operational, even the control.
That is the odd thing about these machines. The machine itself is very well
made, I would say at least twice as heavy as a standard Bridgeport manual
machine. The ball screws are huge. Everything is definitely industrial
strength. The controls were just bad. Just add modern controls and away you
go.

To answer your question about using the DRO sensors in conjunction with the
steppers; No not with a standard setup. The machine operates in open loop
mode. Not closed loop. It is basically up to the programmer not to exceed
the capability of the machine and cause it to loose steps. The nice thing
about the Boss machines is if you retain the mechanical DRO setup you can
compare it to the CNC readout. Any discrepancies will show up there.

Monty

OK Monty Thanks. 

Paul Lamar
 
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