Re: [CAD_CAM_EDM_DRO] Re: Z axis

Where are folks posting newsgroup pics these days? I tried to upload a
couple but the yahoogroups system says the storage area is full for this
group... I'm sure this has been disussed, but the group is so chatty -
I can't find a reference to this topic in 9000+ messages I have
accumulated. (Plus I got side tracked reading messages I had previously
skipped...)

Thanks, Cheers, Peter



mjf462001 wrote:

> Peter,
> I am glad to hear that. I would love to see the pics.
>
> Matthew
>
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., Peter <prenolds@s...> wrote:
>
>>I drive the knee on my CNC mill (BP Clone) and can report good
>>
> results
>
>>although it took a lot of fiddling to get things set up correctly.
>>
> I
>
>>posted questions on alt.machines.cnc and received many of the same
>>helpful suggestions described earlier - i.e. gas springs and/or
>>emergency brake to stop the knee's weight backdriving the ball
>>
> nut. I
>
>>really appreciate having 16" of vertical travel under computer
>>
> control.
>
>>My machine started life with an acme screw for Z but when I drove
>>
> the
>
>>knee up and down at my stepper's top speed (yielding 24 IPM on Z
>>
> axis)I
>
>>got horrible gib vibrations which I couldn't really eliminate with
>>
> gib
>
>>adjustment. (It would just return at different speed.) And I still
>>
> had
>
>>a backlash problem if I ran at full speed - so I installed a ball
>>
> screw
>
>>& nut to see if that would solve the problem.
>>
>>I also purchased two $14 gas springs (75lb each) from McMaster Carr
>>
> (p/n
>
>>9416K403 - mounting fittings are extra)and installed them at the
>>
> front
>
>>of the knee. I'd probably suggest a pair of slightly stronger gas
>>springs (say 125lb) but a combined 150lb of gas spring stops any
>>movement of the knee - even with the stepper motor removed.
>>
> (Though I
>
>>wouldn't stick my hand under it without wood blocks to support
>>
> it...)
>
>>I can post a couple of pics tomorrow if anyone is interested.
>>
>>Cheers, Peter
>>
>>p.s. I've had an excellent experience dealing with Rockford Ball
>>
> Screw.
>
>> They are very well organised.
>>
>>p.p.s. I've also been dealing with Flashcut for a couple of years
>>
> and
>
>>love their little controllers (I have 2 cnc'd machines) and PC
>>
> software
>
>>- they just don't break!
>>
>>
>>
>>Jon Elson wrote:
>>
>> > mjf462001 wrote:
>> >
>> >
>> >>--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
>> >>
>> >>>mjf462001 wrote:
>> >>>
>> >>>
>> >>>>Hugh,
>> >>>>
>> >>>>Thank you for the link. I am still not sure weather
>> >>>>I should drive the quill or the knee. When I get around to
>>
> making
>
>> >>>>
>> >>up
>> >>
>> >>>>my mind I will at least have some pics to reference to.
>> >>>>
>> >>>If you use the machine to drill holes, or if you have some slack
>> >>>in the vertical ways for the knee, like mine, then I think you
>> >>>
>> >>should
>> >>
>> >>>go with the quill. My knee sags out, toward the operator, when
>>
> you
>
>> >>>lower it. I can't tighten the gib because there is a worn spot
>>
> on
>
>> >>>
>> >>the
>> >>
>> >>>ways.
>> >>>
>> >>>Jon
>> >>>
>> >>John
>> >>I saw a pic of Dan's setup. The way he drives the knee, I would
>>
> say
>
>> >>it looks pretty rigid!
>> >>
>> >>Without having to do the math I wonder how much torque a guy
>>
> needs
>
>> >>so he wouldn't have to gear down (slow down) the z axis drive.
>> >>The mill is new and without any wear.
>> >>
>> >
>> > I'm not saying it isn't rigid, just that you are moving a LOT of
>>
> iron to
>
>> > poke
>> > a 10 gram drill bit into a workpiece. On a Bridgeport Series-I
>>
> size
>
>> > machine,
>> > you are talking about moving about 1000 Lbs of iron up and down
>>
> every
>
>> > time. It certainly will work, but it may cause much more rapid
>>
> wear
>
>>on the
>> > knee slide. You should note this is the most highly stressed
>>
> way on the
>
>> > machine, as the weight is completely off to one side of the
>>
> slide.
>
>>Worse,
>> > it puts the load on the dovetail, rather than on the flat!
>> >
>> > I think it is unreasonable to try to CNC the knee without a
>>
> ballscrew
>
>> > retrofit. And, after a ballscrew, you'd need a safety brake to
>>
> prevent
>
>> > the table from dropping when you go to E-stop, or lose power. A
>> > reliable counterbalance, either weights and pulleys or gas
>>
> springs,
>
>> > would help out, but then you'd definitely need a ballscrew, or
>>
> the
>
>> > backlash would show up, without the knee weight.
>> >
>> > Jon
>> >
>> >
>> > Addresses:
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>> >
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>> > List Manager
>> >
>> >
>> >
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>> >
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>> >
>>
>
>
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>
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