Re: [CAD_CAM_EDM_DRO] Re: minimill thoughts was Re: Dead Grizzly speed control/VFD

How big/small do you call a mini-mill?
I've got one in the prototype stage that you can build to whatever size
big/small you prefer.
You can find out more by visiting the DreamMachine egroup site

Smoke

-----Original Message-----
From: Alan Marconett KM6VV <KM6VV@...>
To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
Date: Friday, March 09, 2001 1:27 PM
Subject: [CAD_CAM_EDM_DRO] Re: minimill thoughts was Re: Dead Grizzly speed
control/VFD

>Hi Carlos,
>
>Saw your images, Great! Looks like a fine machine. Just one question:
>When do we get to see the finished goods? And how will you sell them?
>How big?
>
>OK, that was three questions. I'm sure we're all waiting for results!
>14x9x10 would seem to be my "Big Brother" to the Sherline. PLEASE keep
>us posted.
>
>Alan KM6VV
>
>
>Carlos Guillermo wrote:
>>
>> Ballendo -
>>
>> The first problem I ran into when trying to make a long x travel with the
>> conventional configuration (slideways and saddle, ala Bridgeport Series

1)

>> was "tipping over". If you have a table that is too long for its weight,
>> the center of gravity of the entire machine starts getting to close to

the

>> edge of the base footprint. Of course, you could bolt it down, but you'd
>> also have the problem of excessive overhang greatly increasing the loads

at

>> the bearing surfaces (both X and Y). This would, in turn, increase the
>> friction forces at the bearings, requiring stronger muscles/motors, and
>> accelerating wear (again, both X and Y). Now, any slop (both X AND Y) in
>> the bearings will be exaggerated when the center of gravity of the table
>> goes past the end of the saddle, because it will "rock" to the other end

of

>> the slop (the weight of the saddle will delay this a bit). All these
>> problems are made worse by narrow y-axis bearing spacing, and short

X-axis

>> bearing length.
>>
>> I'm trying to avoid these problems in my ground-up machine by using a
>> "bedmill" layout, where the table is shorter than the saddle, and the

y-axis

>> bearing spacing is fairly wide. Ideally, the CG of the table will not
>> travel past the point of rocking the saddle, and since the saddle is

longest

>> and heaviest (reverse of typical knee-mill layout), there is additional
>> margin before the table "teeters". If done correctly, there will never

be

>> enough overhung load to apply a moment to the bearings. The main problem

I

>> ran into with the bedmill layout for a benchtop mill was having a long
>> enough table for fixturing, etc. without ending up with a super long

saddle.

>> I finally ended up with 14x9x10 inch travels (xyz) and an 18 x 8 table
>> (which I hope to leave alone since I'll be sending out the foam patterns

for

>> castings soon). I'm posting images to the files section, in case any one
>> wants to see them ;^)
>>

(http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/CNC%20mill%20design/)

>> Any feedback is welcome and appreciated.
>>
>> Carlos Guillermo
>> VERVE Engineering & Design
>>
>> Ballendo wrote -
>>
>> What I can't figure out is why
>> everybody makes the x axis travel so short (about 9 inches). Joe M at
>> sherline says its because the extrusion warp and twist becomes
>> excessive to machine away in longer lengths, but what's the grizzly
>> excuse? poseidon? Prazi? MaxNC (could be same as Sherline)? REX?
>> Myford? Shipping cost of the extra cast iron?
>>
>> Wm. Dubin and I have had an offlist(sherline list) conversation
>> regarding a "bigger" sherline, but still little. Like a sherline with
>> a 3 slot table (same spacing) and a 7 inch Y (2000 mill base) and a
>> 12 inch X? I bet the person who brings this (or something like it in
>> cast iron) to market will do well!
>>
>> The MaxNC 15 is close, but pretty expensive. And that lousy motor
>> setup, IMO.
>>
>> Ballendo
>>
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>Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the

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>
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