Re: [CAD_CAM_EDM_DRO] scraping beds for long tables

Hi Sven:
I believe that your way (scraping the table ways dead flat) is the
better way.
I believe this because you can't compensate for varying table loads anyway,
so if a machine is scraped to have proper contact for a heavy overhanging
load, it will be incorrect for a well-centered lightweight load.
On a typical kneemill, there are so many other factors that contribute to
machine inaccuracy, that the whole business of trying to compensate for
offset table weight is foolish unless you also pay attention to the Y axis
and the Z axis.
Your best chance of achieving consistent machine performance over a variety
of normal conditions is to do exactly as you are doing now: Give the table
maximum possible support in the unloaded condition by making everything as
flat and even in contact as you can.
If you need super precision in the machine, then a machine with an
overhanging table is not a good choice anyway; you need a bedmill with a
short table travelling on long bedways (like the Okuma Vertical Machining
Centers).
Cheers

Marcus
-----Original Message-----
From: Sven Peter, TAD S.A. <peteryco@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>;
cnc-de@yahoogroups.com <cnc-de@yahoogroups.com>
Date: Sunday, July 15, 2001 6:55 PM
Subject: [CAD_CAM_EDM_DRO] scraping beds for long tables

>Dear friends,
>I am pleased that it turned out that there are quite a few persons here
>who scrape bed ways.
>I have a question I have for a long time and nobody was able to
>respond satisfactory till now.
>When my father initialized me in scraping and later in a practice
>I was told that for a bed of a long travelling table (example x table of
>a
>Bridgeport that has a short bed) you should scrape into the bed
>a curve so that the curve counter arrests the weight of the table
>when it travels far out.
>Because I never got an instruction about it how to make it well
>and because I saw in quite a few mills that this curve was made too
>deep.
>(with the result that the flat parts of the dovetail way are very much
>worn
>at the tips and in the centre the table not even touches the bed
>so that the oil oil pours out like nothing.)
>
>Therefore I never made it in any of the machines I rebuilt.
>Instead I preferred to leave the bed straight and with
>as much as possible support area. Anyway in all cases the bedways were
>so
>worn that the improvement of a wrong scraped bedway was significant
>against before the worn one.
>I preferred to have a little error than a wobbly machine that wears out
>fast.
>Who can tell me how it is done right?
>Thanks a lot
>Sven Peter
>
>
>[Non-text portions of this message have been removed]
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
>Post messages: CAD_CAM_EDM_DRO@yahoogroups.com
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...
>Moderator: jmelson@... timg@... [Moderator]
>URL to this page: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>bill,
>List Manager
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>