Hi all,
Everyone has their own favorite way of workholding. Without good work
holding nothing good follows. Thin angle stock I clamp in the vise with
a rectangular block as suggested below. However, my most common approach
is to bolt it down usually with 1/4" shcs, which implies gr 8. If I
think I need better position control then drill and ream for dowel pins
at +.0005 to +001" plus bolts to hold vertically. Or since 95% of my
work is with steel, or if I get frustrated just weld it to a plate which
get bolted to the bed. Good workholding burns a lot of time but is
absolutely necessary. Duh!
Milling cutters: usually TiAlN sans coolant. I've not tried AlCrN coated
but a local machine shop is getting a mile of path length/cutter! That
is a lot of chips.
Speeds and feeds: what every you can get away with. With my little
machine (BP size 1963 vintage) 0.05" axial is about all I can get with
out it screaming at me. But I will use as much doc as I can get without
screaming.
I still have no solution for the needle sharp chips I get with
conventional cutters.
Cutter comp = yes. Rough with tool dia 0.04 over the real dia. Hard to
get in trouble that way. Edit tool table or change tool number for
successive passes.
Spring pass as necessary.
Chip removal: compressed air or vacuum or both like the dental hygienist
does for cleaning. OK for one-offs but production needs a better idea.
That's my tuppence; machining is an adaptive and dynamic process.
Dave
On 8/4/21 6:54 AM, Cristian Bontas wrote:
Hi
I would do it about the same way you did it first, with a few changes.
First, clamp it as high as possible on the vertical part. Get rid of
the cylinder, or if the vise is not clamping properly without, use a
thinner one (say 6-8 mm diameter) placed as close to the upper lip as
possible.
Support the horizontal part. Assuming the top of the vise below the
overhanging part is flat and horizontal, make a small block to support
it. Clamping the part would start with pressing it on this block, then
tightening the vise. Make a long clamp to press down on the part over
the block - might need to use two screws on either side of the vise.
Place a bit of Al or Cu wire between the part and the clamp, as at
this length it will bend. Machine the part in several cuts, so that
you can move the clamp and support block so that they don't interfere
with the cutter and its holder.
On 8/4/2021 00:27, John Dammeyer wrote:
That's a good suggestion John F. Thanks. I did do some more playing
around and it's clear the part flexing and the backlash both were at
fault especially with the plunge to the next depth.
And that brings up another issue. One of my pet peeves with
electronics project magazines is they are great at a schematic and
either point to point wired or PC board but very little energy is
spent on describing various ways of mounting or installing in a
cabinet. Especially with the concept of Human Factor Engineering
which is the practice of making something easy to use or even
intuitive. Like an ESTOP button is always a red mushroom Not a
toggle switch.
Same goes with work holding. Youtube has tons of videos that show a
tiring sequence of a milling cutter sprayed with coolant making chips
for 3 minutes with 3 commercials interjected, one every minute. But
very little on work holding.
The next part I am making is shown in the attached screen shot
rendering. My raw material is in the second photo. So the question
is about work holding and how or what features of LinuxCNC can be
used to make this easier.
I can use my band saw to create the initial width and split it into
two L shapes. But after that I start to have problems, due to lack
of experience I think, on how to firmly hold it and mill the stuff
with a 5mm and 6.35mm (1/4") cutter.
Suggestions?
Thanks
John
-----Original Message-----
From: John Figie [mailto:zephyr9...@gmail.com]
Sent: August-03-21 11:59 AM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Something went wrong.
Speaking of backlash. My tiered old Bridgeport has about 0.002" of
backlash
in the ballscrews. So if circular interpolation is used there is a
small
bump at each 90 degrees of the circle. But if I make the finish pass
first
clockwise and then repeat counter clockwise the imperfections are much
smaller. I know from experience with my first CNC machine that's
built that
actually used leadscrews with lots of backlash the clockwise
followed by
counter clockwise method was remarkable compared to a single direction
final pass.
John
On Tue, Aug 3, 2021, 10:10 AM jrmitchellj <jrmitche...@gmail.com>
wrote:
You might try the run again without the backlash compensation in
LCNC to
get a feel of what it is actually doing.
--J. Ray Mitchell Jr.
�I predict future happiness for Americans, if they can prevent the
government from wasting the labors of the people under the pretense of
taking care of them.�
THOMAS JEFFERSON
On Tue, Aug 3, 2021 at 6:24 AM Gene Heskett <ghesk...@shentel.net>
wrote:
On Tuesday 03 August 2021 05:31:56 andy pugh wrote:
On Tue, 3 Aug 2021 at 07:58, <marcus.bow...@visible.eclipse.co.uk>
wrote:
I draw all this from my own ballscrew conversion of my own mill,
some 20 years ago. If I was doing it again, I would use two nuts,
with spring tension between the pair
Springs might not be the best way. The common way to tension double
nuts is to (basically) screw them into each other and lock the
angular
relationship.
You _can_ get preloaded single nuts, using oversized balls. That
only
works if the ball track is the right shape, though, it needs to be a
4-point contact shape.
Which I'd suspect as being subject to rapid initial wear until it was
just a normal screw with about a thou of backlash.
For me, I bought C7 grade which may have 2 thou but in several
years has
not gotten significantly worse. Protecting the screw from
contaminants
is the most important thing for long life. On my Sheldon, the Z
screw, a
1450mm long 25mm C7, got sealed bearings on both ends, a collar to
clamp
a bellows to on both ends of both sections, and 2 of the 6 mounting
holes in the nut were drilled all the way thru so air could get
from one
side of the nut to the other as the nut moved. The nut gets one
pump of
grease a year. Backlash, some of which is in the end bearing, was
about
1.9 thou 5 years ago and still is. It has not been uncovered in that
time. I don't have a bellows on the x screw but its channel in the
carriage is sealed top and bottom unless the carriage is clear in.
exposing the screw behind the QCTP boss. No compound since LCNC is
better than mechanical you set by eyeball. Plus it was busted from a
fallover when I bought it. I keep a rag over the slot in that event.
That faint thumping? Me, knocking on wood, no swarf has gotting
into it
yet...
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law
respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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