Re: [CAD_CAM_EDM_DRO] Z axis on the knee, how practical????

As Tim and others have mentioned, the knee could care less if you lean
on it stand on it - or not. If you are in the way it WILL push you out
of the way without any hesitation... All CNC machining has moving parts
that you have to get used to - whether it is the knee or the quill or
the table or saddle.

I too have experience with 5" of CNC quill travel on another small
machine (Rong Fu) and the whole reason I researched and went with
CNC'ing the knee on this machine was because I do a lot of 3D
(contouring and do a lot of tool changes usually starting with a 3/4"
end mill and finishing up with a 3/8" or 1/4" ball end mill. With
significantly different tool lengths you just can't accomodate tool
changes within your work envelope in 5" of quill movement - due to the
3" to 4" of clearence required to change an R8 tool. With the knee
CNC'd it is easy to move to a tool change position, swap tools and hit
go - all without losing position. I just use a 12" height gauge to
measure and program offset tool lengths from an R8 taper I turned on the
lathe.

As my mill did not have a gas lift like Tim's Bridgett, based on someone
else's suggestion, I purchased Suspa brand air springs from McMaster
Carr ($15 ea) and fitted them on the sides of the knee. In 9 months of
pretty regular use, thay haven't missed a beat and because there are
two, I have a degree of redundency should one fail. I should also
mention I have Rockford ballscrews fitted on all 3 axes.

I run a direct drive stepper on the knee which is rated at 1869oz-in
purchased from Mendonet at: http://www.mendonet.com/steppers/nema42.htm
and have been very happy with the motor (pricy, but good). I can get
about 30 IPM rapids with the knee and have not needed anything more than
that. Little G201 Geckos drive all 3 axes. A servo based system
(appropriately sized) would give you faster rapids if that's what you want.

I can't see how moving the knee would have anything to do with part
visibility - everything gets covered with chips anyway. You can't see
much until you brush/blow the chips away. When you are peering at your
work as it is being machined - just make damn sure you have saftey
glasses on - in case something pings in the direction of your eyes.
Personally, I don't like getting so close during roughing operations
metal removal rates are quite high and chips really fly!

Cheers, Peter


Tim Goldstein wrote:

> Bridgett does not care if I lean on the table while she works. For that
> matter she doesn't care if I jump up and dance on the table as long as I
> have the air assist on. Just moves to where she is suppose to go. My
> Shoptask is a driven quill so I have experience with both. The knee
> moves plenty fast, but it is not a problem, but something different to
> get used to.
>
> Tim
> [Denver, CO]
> Close out stepper drives, encoder, stepper motors
> http://www.KTMarkting.com/CNC.html
>
>
>>-----Original Message-----
>>
>>
>>Group,
>>
>>I've been following the discussion of Z-knee conversions. I
>>understand why this is done...because it's easier than fitting a ball
>>screw to the quill.
>>
>>My question involves what it's like to machine parts on a B'port or
>>larger machine with the Z on the knee. Personally, I can't imagine
>>it would be a desirable situation. First off, sometimes I lean on
>>the table as a part is being cut, that wouldn't be possible with the
>>table moving up and down. How about part visibility, isn't it hard
>>to closely watch the cutting action if the part is moving up and down?
>>
>>So, tell me what it's like. Are you guys who are doing this type of
>>conversion experienced with more conventional Z axis (quill) machines
>>or don't you have any basis for comparison? Maybe the Z-knees move
>>so slowly there isn't a problem?
>>
>>just curious,
>>
>>Doug
>>
>>
>>Addresses:
>>FAQ: http://www.ktmarketing.com/faq.html
>>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>>
>>OFF Topic POSTS: General Machining
>>If you wish to post on unlimited OT subjects goto:
>>aol://5863:126/rec.crafts.metalworking or go thru Google.com
>>to reach it if you have trouble.
>>http://www.metalworking.com/news_servers.html
>>
>>
> http://groups.yahoo.com/group/jobshophomeshop I consider this as a
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> OFF Topic POSTS: General Machining
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> http://www.metalworking.com/news_servers.html
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> http://groups.yahoo.com/group/jobshophomeshop I consider this as a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
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