Bridgeport (was : no subject)

Howdy Doc,

if you look at any tool, the proper size bits for the tool, proper
belt/gear, matched to the torque required to do the work.

Bridgeports are belt driven.

When a VERY close timing is required, like in threading that matches
the spindle speed to the cutter, gearing is needed.
most lathes use gearing to match X and Y travel to spindle rotation
for just that reason.

if you want a used Bridgeport, start calling around. I missed a deal
from a shop that GAVE AWAY their old units to make room for the new
CNC milling centers they bought.

I also came across three Bridgeports for $2,000 each with DROs and
power feed. And in my searches, I was told that if you look hard
enough, you can find an old Series one with servo's.

Good luck.

Dave

--- In CAD_CAM_EDM_DRO@y..., "docholliday01201" <whollid1@m...> wrote:
> A general machining question if you don't mind.
>
>
>
> Over the last three years I have completely worn out the
> sherline milling machine. Over the last one year I have developed
> the CNC conversion to its fullest degree on this machine. However
> over three years of use the X axis ways are completely destroyed.
As
> well the machine is quite small for what I wish to do. So I find
> myself browsing for a new machine.
>
> Two general options come to mind: one would be a full-size
> used Bridgeport milling machine, or Bridgeport clone. Which I
would
> slowly convert to servo based CNC controls, likely using gecko
> drivers,EMC , and servo motors purchased from Ebay. The other
> options is one of the Chinese benchtop milling machine's. What I
do
> not understand is the functional difference between a gear head
> machine, versus a belt driven machine. For equivalent hp ratings
> there appears to be about $300 difference between equally equipped
> machines. I understand the gear head allows for more rapid
spindles
> speed changes but I do not understand the claims of more stable
> spindle speeds. I could see if there was gross belt slippage this
> would be an issue. But I do not understand in general usage how
> driving the spindle by means of gears produces any more efficient
> drive than the use of a belt. I understand from engineering that
the
> gear drive is more efficient than a belt, but very slightly so . I
> could see if this were to be a CNC application where the motor was
to
> have an encoder. But a very slight wavering of the spindle speed
> should have no functional difference in machining.
>
> Any thoughts anyone has, especially comments from individuals
> who have used both machines would be appreciated
>
> The likely application of this machine would be making something
> along the lines of go cart parts, radio control car parts or the
like.