Great !
You note that the quill does not move in xy when pressed on. Everything
locked.
Impulse inxy, in line with x or y ways.
I would expect at least 0.04 mm of movement, from bend from the column.
That is about what I get, and that is about what a Bridgeport series 2,
CNC, a very heavy and stif mill gets.
To test, I suggest chucking a max capacity drill rod in the quill, and
push on that, just like an end mill does.
Approximate forces in milling (machien mass):
1/2 Hp minimills - MT2/MT3 sockets - 20-50 kg - ( 2-300 kg)
3/4 Hp industrial, old Bridgeport M-heads - MT2 sockets - 50-100 kg (800 kg)
1 Hp industrial - Bridgeport Series 1, R8 collets - 100 kg ( 1000 kg)
2 Hp Hobby R8 collets - 50-100 kg (400-600 kg)
2-3 Hp Old Industrial -Bridgeport Series 2 - R8 - 100-200 kg (2000 kg)
3+ Hp Modern Industrial - ISO30 - 300-1000 kg (10.000 kg)
Collets rigidity - Spindle ridigidty - Machine rigidity - Available Hp -
Usable Hp - Material removal rate are all inter-related.
These are all in-line ... Ie
A best known example of an MT2 milling machine, Bridgeport M-head,
ciraca 1930-1960, had a 3/4 Hp industrial 3-phase motor.
It used a MT2 socket.
The socket becomes the limiting factor, and a mill like that cannot
effectively utitilise more Hp than about 1 Hp.
This head is more acurate, and more rigid, and better made, than any
modern hobby milling machine head, using an MT2 socket.
In the case of a modern hobby machine, lightweight, even though it uses
an R8 rosket, the machien itself does not have the rigidity required to
fully utilise either the R8 collets capacity, OR the Hp often supplied
with it.
So some small hobby mills, supplied with R8, and say 2HP, cannot by any
means utilise as effectively large end mills as the same R8 socket on an
industrial, old, mill like a Bridgeport Series 2.
In this case, the light modern mills are not meant for industrial
production, as the old Bridgeport ones were.
The differences between rigidity and Hp are about 3-4:1.
Ie a typical mill, compared to a best in breed, will have about 4x more
rigidity in the best vs. the typical example.
Both sockets, and machine mass, are an excellent indicator of machine
rigidity.
One more thing:
Machine design affect the rigidity about 3-5:1.
A knee mill is about 5x less rigid than a portal mill with a moving
table, of the same size.
A portal mill is the most rigid design known.
The moving tabel one will needs be about 1.5-3x as heavy, with 1.5 being
necessary and 3x being typical, as it makes it more accurate.
It also needs twice the size, because a movign table only has half the
usable area of the table.
My mill is a moving table portal design, in steel.
Welded, bolted construction, 1600x1600 in size, 2000 kg.
Head is a Bridgeport M-head, original 3-phase motor, driven by Hitachi VFD.
Resolution (Accuracy) is about 4x original Bp, about the same as a
Bridgeport Series 2, or about 0.01 mm.
Resolution/Accuracy is achieved by using industrial linear guides, THK
20 and 25 mm size. Movement is by ballscrew, of low grade rolled type.
I do not currently have locks, or swarf guards on the ways, which I am
making.
> This is another in my series for people new to our hobby. It suggests
> a set
> of test that will assess the sloppiness of a given mill. Most of these
> tests
> can be performed without applying power and might help a person avoid
> buying
> a machine beyond help. It might also help a person see the beauty in a
> machine that just looks beyond help.
>
> If you are interested, please see
>
> http://rick.sparber.org/mt.pdf
>
> I welcome comments and questions. In fact, I'm depending on input from our
> experts to correct what I have written and supply additional tests
> that are
> easy to run. All of us are smarter than any one of us.
>
> Rick
>
[Non-text portions of this message have been removed]
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