26 Aug
2011
26 Aug
'11
12:35 p.m.
On Fri, Aug 26, 2011 at 1:45 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Assuming that's one of those '3D printers'. I doubt it has the resolution
to make something like this.
It does not (as I mentioned in my previous message that you might not
have seen), *but* I may have an alternative method to use this
technology.
... one of those Alps 4-pen plottre mechanisms.
Unfortunately,
as wityh many such plotters, the motor pinion gears have split with time,
so it's not useable at the momnet, I should have a go at cutting soem
replacements...
? ?Sounds like it's RepRap time.. The pinions are about 3mm overall diameter
Yes.
and have perhaps 10 or 12 leaves (teeth to the rest of
you ;-))
Something like that, yes. I don't recall the precise number and can't
find the previous discussion threads that have happened on this list
over the years.
I realize that to a trained machinist with the right tools, cutting
gears is just another day on the job. I am very much a novice when it
comes to lathes and mills. To me, cutting a gear that's 3mm across
the face is a serious challenge. It's also time consuming - paying
someone else to do it starts to get rather expensive (at two pinion
gears per mech). The size is a bit on the small side, but it may be
possible to order printed gears made from sintered metal from
Shapeways. Their requirements are that all dimensions be 2.5mm or
larger. This gear barely qualifies.
If someone just happens to have an STL-format file of this gear,
that'd be terrific, but if not, if one has a 2D image of the face of
the gear, OpenSCAD or, now, the Shapeways website itself, can easily
extrude a flat outline to a 3D version of the silhouette. One such
tool for generating (self-described low precision) gear patterns is
here:
http://woodgears.ca/gear_cutting/template.html
... and I'm sure there are many others.
Shapeways charges by the cubic centimeter of material used. There's
not much volume in a 3mm-diameter gear with a 1.3mm-diameter hole in
it - my first estimate is under 20 mm^3 (a cube 3mm on a side is 27
mm^3 after all). You could fit 27 gears in 1cc with lots of room to
spare, and 1cc of Shapeways "stainless" bills at $10 with no apparent
setup fees for standard finishes.
I haven't handled any of Shapeways' metal products, but I'm imagining
a surface smoothness based on the grain size and the laser focal point
diameter and the stepper resolution, but until clarified, I'd consider
300dpi to be a starting point for estimation purposes. One can do
some shaping and smoothing work after the printing process, naturally,
but the less of that required, the better.
So is there anyone here who has the CAD skills to draw a gear, or at
least sufficient skills as a machinist to completely and adequately
describe the critical parameters for someone else to work from? I
think it could be inexpensive to do a run of a handful of gears
through Shapeways. Because of the strictly functional nature of the
part, there should be no worries of trademark or other IP
infringement, to head that discussion off.
I can bang out something that's close, but I don't believe I have the
skills to evaluate if my attempts would be close enough (specifically
something that's going to fit on the motor shaft and not chew up the
next gear in the train). Is there anyone here willing to draft a gear
profile or at least parametrically describe the gear in terms suitable
for reproduction? If so, I can see about taking that beginning to the
next stage.
-ethan
26 Aug
26 Aug
1:42 p.m.
On Fri, 26 Aug 2011, Ethan Dicks wrote:
On Fri, Aug 26, 2011 at 1:45 PM, Tony Duell <ard at
p850ug1.demon.co.uk> wrote:
Assuming that's one of those '3D printers'. I doubt it has the resolution
to make something like this.
It does not (as I mentioned in my previous message that you might not
have seen), *but* I may have an alternative method to use this
technology.
If you can get me the specs on the gear, I can make a model of it in
Inventor. I'd start with a flat pattern made in Gearotic
(http://www.gearotic.com) and then go from there. Ponoko offers similar
services to Shapeways.
g.
--
Proud owner of F-15C 80-0007
http://www.f15sim.com - The only one of its kind.
http://www.simpits.org/geneb - The Me-109F/X Project
Some people collect things for a hobby. Geeks collect hobbies.
ScarletDME - The red hot Data Management Environment
A Multi-Value database for the masses, not the classes.
http://www.scarletdme.org - Get it _today_!
Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rabidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a turd
by the clean end.
... one of those Alps 4-pen plottre mechanisms.
Unfortunately,
as wityh many such plotters, the motor pinion gears have split with time,
so it's not useable at the momnet, I should have a go at cutting soem
replacements...
? ?Sounds like it's RepRap time.. The pinions are about 3mm overall diameter
I can bang out something that's close, but I don't believe I have the
skills to evaluate if my attempts would be close enough (specifically
something that's going to fit on the motor shaft and not chew up the
next gear in the train). Is there anyone here willing to draft a gear
profile or at least parametrically describe the gear in terms suitable
for reproduction? If so, I can see about taking that beginning to the
next stage.
1:42 p.m.
I am one of those that makes the real thing TM, at those sizes I dont
expect quality from cheap 3d printing.
when I get the 5 axis powered up I could generate one if someone gives
me the dimensions.
or possibly an excuse to get the hobbing machine working.
Another job on the list is to add spindle feedback to the 5 axis mill
then it too can hob gears.
For some one offs I just dremel up a flycutter and hack some standard gcode
then let the 5 axis handle it as :-
http://www.youtube.com/watch?v=HAtziCsUj5Q
At these sizes and duty cycle one can get away with a few inaccuracies
http://gears.archivist.info/gears/index.html
Dave Caroline
2:44 p.m.
On 26/08/11 20:35, Ethan Dicks wrote:
So is there anyone here who has the CAD skills to draw
a gear, or at
least sufficient skills as a machinist to completely and adequately
describe the critical parameters for someone else to work from? I
think it could be inexpensive to do a run of a handful of gears
through Shapeways. Because of the strictly functional nature of the
part, there should be no worries of trademark or other IP
infringement, to head that discussion off.
Well I'd be interested in a few of these to keep as spares -- I have a
Sharp CE-series plotter which is basically an Alps plotter mech bolted
onto a Sharp controller board. CE515P or something like that.
... But what I'd REALLY be interested in are a few of those blasted
pens! I can probably machine some adapters and so forth on the lathe,
but I've never -- not even once -- seen a pen refill which was short
enough to fit in the holder.
I suppose the ideal would be something like a Rapidograph nib mated to
an ink reservoir, but those things seem to be prone to blocking if you
leave them open on the table.
Though that said, if Laszlo Biro managed to make a ballpoint pen in
1938, it should be possible to produce something similar with modern
machine tools. Getting the viscosity of the ink 'just right' might be a
bit of a pig though.
Cheers,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
27 Aug
27 Aug
10:42 a.m.
... But what I'd REALLY be interested in are a few
of those blasted
pens! I can probably machine some adapters and so forth on the lathe,
but I've never -- not even once -- seen a pen refill which was short
enough to fit in the holder.
I wonde if you could cut down a longrefil and remove a little of the ink
frm the cut end so it doesn't all leak out. And put that in a home-made
adapter.
Though that said, if Laszlo Biro managed to make a ballpoint pen in
1938, it should be possible to produce something similar with modern
machine tools. Getting the viscosity of the ink 'just right' might be a
bit of a pig though.
I wondef if you culd dismantle one of the old pnes non-destructively and
refil it with ink. That would give you the bllpoint part. Of course it
doesn't help in gettign thr right viscosity of ink.
-tony
10:24 a.m.
and have
perhaps 10 or 12 leaves (teeth to the rest of you ;-))
Something like that, yes. I don't recall the precise number and can't find the previous discussion threads that have
happened on this list
over the years.
I realize that to a trained machinist with the right tools, cutting
gears is just another day on the job. I am very much a novice when it
There are basically 2 ways to cut such a pinion.
The first used s a special milling cutter which is the shape of the cabe
ebtween the teeth. You turn a piece of rod the overall diamater of the
gear in a ltathe, and then put that rond in a dificing head. Using the
milling cutter you cut one of the inter-tooth gaps, then using the
dividning head you turn the rod throug the appropraite angle (1/12th of a
revolution if there are 12 teeth, etc), then cut the next gap and so on.
The problems are that the milling cuttter is strictly only correct for
one particular pitch _and number of teeth_ For geears of the same pitch
-- that is ons that you would mesh together, the inter-tooth gap does
change as the number of teeth changes. Normally, an apporximation is
made, the cutters some in sets of 8, ech oovering a range of numbers of
teeth. THese cutters are not cheap either. I've been quoted over \pounds
50.00 for one. No, not a set of 8, one cutter.
On something this small, you would have to take very light cuts to
avoid bending the workpiece (the rod you're making itn oa pinion), which
would slow things down a bit.
The second way is claled 'hobbinh'. Here the cutter is called a 'hob',
and is a bit like a thread-cutting tap. It is rotated, the workpiece is
also rothated at the right speed to cut the apporirate number of teeth
[1]and the 2 a brought together. Think of it as being a bit like a
worm-and-wheel drive wit hthe 'worm' actually cutting teeth in the wheel.
This needs more specialised equipment (a hobbing machine is only used for
gear cutting wheras a lathe. mill and dividing head have many other
uses), but the greatadvantag is that one hob cuts all gears of a given
pitch no matter the number of teeth,
[1] Ol;der hobbing machines did this mechanically usinga gearbox with
selectable rations (ofthen by using changewheels that you haf to fit the
right comibnation of). There have been designs using a steppre motor to
roate the workpiece contoller by a shaft encoder on the hob spindle and
some suitable electroncis. I really must have a go at making one...
through Shapeways. Because of the strictly functional
nature of the
part, there should be no worries of trademark or other IP
infringement, to head that discussion off.
I can't see how there could possibly be legal problems for soemthing like
this.
-tony
4866
days inactive
4867
days old
5 comments
5 participants
participants (5)
-
ard＠p850ug1.demon.co.uk -
classiccmp＠philpem.me.uk -
dave.thearchivist＠gmail.com -
ethan.dicks＠gmail.com -
geneb＠deltasoft.com