[Dennis]

I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

[[email protected]]

On Sat, 17 Mar 2012 20:26:54 +0800, "Dennis"
wrote:

I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

Cheap allthread will have pitch errors. Over a certain distance,
decided by the maker, the movement will even out. Does this error
occur everywhere on the screw? If you program a movement of 25mm does
the machine only move22.5mm? I bet it doesn't. If the screw really
only moved .9 to .95 of what it should then the pitch would be off by
..002" to .004" per thread. This amount of error would cause the screw
to bind in the nut. Of course, it really doesn't matter that much
since the machine is CNC. You just program it to make up for error.
Many of the most accurate positioning machines do exactly this. The
machine is moved and the movement mapped. Then the map of position
error is used by the control to adjust the movement of the machine so
that it moves the desired amount.
Eric

[Paul Drahn]

On 3/17/2012 5:26 AM, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....


How much does the leadscrew, itself, move when torque is applied? Some
movement must be caused by the thrust bearings at the ends of the leadscrew.

Paul

[Pete C.]

Dennis wrote:

I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.

I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.

With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?

ACME leadscrews are on the drawing board when finances are willing....

Yep ordinary all-thread isn't particularly precise. You can do screw
mapping to compensate for the pitch error to some extent. Backlash
compensation is more difficult so try to use an anti-backlash nut setup
and ensure solid mounting of the leadscrews. ACME screws aren't
particularly expensive from ENCO or MSC.

[Joseph Gwinn]

In article ,
"Dennis" wrote:

I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

As others have said, allthread isn't all that precise (unless threads
are cut).

However, there is a trick from Roland's Ruling Engine (invented in 1882
to make diffraction gratings): Use a very long elastic nut, so it
averages leadscrew errors out. Rowland used oiled wood, but PTFE ought
to work.

http://books.google.com/books?id=8eI...=PA152&dq=rowl
and+ruling+engine&source=bl&ots=tE9IMY8kn4&sig=9RN phQ9npM6RwhdN13y2KHZWEO
8&hl=en&sa=X&ei=pMhkT9OUB-XE0QHJ_PXMCA&sqi=2&ved=0CFYQ6AEwCA#v=onepage&q=
rowland%20ruling%20engine&f=false

Joe Gwinn

[Ignoramus13020]

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

i

[Bob La Londe[_2_]]

"Dennis" wrote in message
. au...
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm
or 0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

Precision Acme screws will be better, but there is an old feature in Mach
that says you can map your lead screws. I have not tried it yet, and there
does not seem to be much documentation on it. Also, you can calibrate steps
to your leads if they are off or unknown pitch. I have done that. Its
pretty easy with a dial indicator.

[anorton]

"Dennis" wrote in message
. au...
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm
or 0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....


As others have said all-thread is not accurate, but it is not quite that bad
over such a short distance. How is your stage made? It seems more likely
that there is some wobble in yaw or pitch that causes a difference in
position between where the nut is and where thee indicator measures. Also,
if the threaded rod is not straight, it will exert lateral and vertical
forces on the stage versus rotation angle that may cause such a wobble.

[Robert Roland]

On Sat, 17 Mar 2012 20:26:54 +0800, "Dennis"
wrote:

when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0

That is a massive 10% error. It might not be visible to the naked eye,
but it can't be far off. If you examine threads with a plain thread
gauge, you should easily be able to detect such large errors.

I don't know how accurate allthread is supposed to be, but I cannot
possibly imagine an error this large is within specs.
--
RoRo

[Larry Jaques[_4_]]

On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)

--
The greatest justice in life is that your
vision and looks tend to go simultaneously.
-- Kevin Bacon

[Ignoramus13020]

On 2012-03-18, Larry Jaques wrote:
On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


I would first suspect the software, config and control system. Then
like you said, mounts etc.

i

[Pete C.]

Ignoramus13020 wrote:

On 2012-03-18, Larry Jaques wrote:
On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


I would first suspect the software, config and control system. Then
like you said, mounts etc.

i

The software, config and control system are the least likely suspect. If
the steps/mm setting was off the distance the axis moved would be off,
but would still be consistent, not jump around. Realize that the OP is
working in mm, not inches so his deviation is 0.1mm which I think is
within the expected tolerance of rolled all-thread.

[Dennis]

"Dennis" wrote in message
. au...
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm
or 0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



OK - THANKS for all the replies, there's a lot to think about!

I got stuck doing other things so I've not had a chance to "play" with the
machine again.

From reading all your replies I think the approach I'll take is:

1) Recheck all lead screw bearings / lead-nut mounts for tightness & play.
2) Check lead nuts for play (these are fairly tight)
3) Use dial gauge & check translation at 1mm increments over 10mm or so.

[Dennis]

"Gunner Asch" wrote in message
...
On Sat, 17 Mar 2012 18:16:46 -0700, Larry Jaques
wrote:

On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and
the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see
0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see
the same values.

What do people think? I guess this is typical for cheap bit of
allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


Ive got some used but ok double angular contact thrust bearings and
housings. Hole is about 10 mm.

Gunner



Many thanks for the offers Gunner - I'm in Oz so shipping etc would likely
outweigh benefit. Offer is much appreciated anyway.

Just had a play in the shed:

http://www.youtube.com/watch?v=FwrWbG7wZnA

http://www.youtube.com/watch?v=4eumURX6S9w

www.youtube.com/watch?v=byYxS12dy5w

[Dennis]

"Larry Jaques" wrote in message
...
On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see
0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


Thanks for the offer Larry, unfortunately I'm in Oz so the shipping etc
would likely be a killer.

There's an eBayer in Eastern Australia who has Chinese ballscrews cheap, but
I'm even cheaper so I'm looking at some ACME leadscrews.

I'm using the SBR16UU bearing blocks, the quality is not the best, but
probably good enough for my needs.


I jst had a play in the shed, still a long way to go but it's working.....

http://www.youtube.com/watch?v=FwrWbG7wZnA

http://www.youtube.com/watch?v=4eumURX6S9w

www.youtube.com/watch?v=byYxS12dy5w

[Larry Jaques[_4_]]

On Sat, 17 Mar 2012 20:34:22 -0500, Ignoramus13020
wrote:

On 2012-03-18, Larry Jaques wrote:
On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


I would first suspect the software, config and control system. Then
like you said, mounts etc.

If it was always off and always the same, I'd suspect the conversion
point he set in the software, but since it changes, I suspect loose
parts.

--
The greatest justice in life is that your
vision and looks tend to go simultaneously.
-- Kevin Bacon

[Bill[_42_]]

On 3/18/2012 5:40 AM, Dennis wrote:
)


Thanks for the offer Larry, unfortunately I'm in Oz so the shipping etc
would likely be a killer.

There's an eBayer in Eastern Australia who has Chinese ballscrews cheap, but
I'm even cheaper so I'm looking at some ACME leadscrews.

I'm using the SBR16UU bearing blocks, the quality is not the best, but
probably good enough for my needs.


shipping small items that will fit in a flat rate envelope (about 10
inches max length) or a flat rate box (up to about 17 inches for the
longer one) is not too pricy. and if the weight is not too much, it's
reasonable, it's when you want to ship something heavy.

The other way to get things from the US to Australia is to find someone
going there on vacation or business who will carry it

[[email protected]]

In the US, some of the hardware store threaded rod is way off nominal and,
suprisingly, some is quite close. Sampling different suppliers has been
worth while.

Hul

Dennis wrote:
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws and
PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm or
0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I see
the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

[Larry Jaques[_4_]]

On Sun, 18 Mar 2012 08:05:57 -0700, Bill
wrote:

On 3/18/2012 5:40 AM, Dennis wrote:
)


Thanks for the offer Larry, unfortunately I'm in Oz so the shipping etc
would likely be a killer.

Airmail from China cost $159 for roughly 48 pounds. Returning my
shipment would have cost roughly $600 via FedEX, UPS, or DHL. The USPS
could do a 5 pound return for only $185! Any time I purchase from
China in the future, they will have a clause about excessive return
costs and seller pays if he wants it returned. (I wonder if he could
have done a pickup for that same $159 he paid. I'll have to check.)


There's an eBayer in Eastern Australia who has Chinese ballscrews cheap, but
I'm even cheaper so I'm looking at some ACME leadscrews.

I'm using the SBR16UU bearing blocks, the quality is not the best, but
probably good enough for my needs.


shipping small items that will fit in a flat rate envelope (about 10
inches max length) or a flat rate box (up to about 17 inches for the
longer one) is not too pricy. and if the weight is not too much, it's
reasonable, it's when you want to ship something heavy.

The other way to get things from the US to Australia is to find someone
going there on vacation or business who will carry it

Shipping halfway around the world is outrageous! My entire M3 of
Jarrah only cost $400 to ship here from Oz. 'Course, I had to go to
Long Beach to pick it up.

--
The greatest justice in life is that your
vision and looks tend to go simultaneously.
-- Kevin Bacon