Re: [Emc-users] Making a steper pulse generator, would like comments

[Chris Albertson]

Yes the faster you go the bigger the jumps.   With my 1MHz clock I can
only make pulses with periods that are a whole number of microseconds.

So I ask again:  What is the fastest step rate you actually use with a
real machine?

What is needed?  Do people run motors at 100,000 steps per second?
What I'm guessing is that it is rare to run as high as 10K steps per
second.I could be wrong, so I'm wanting to hear from people who
are running real machines.

To say this using  MK or LinixCNC terminology what is the fastest
usable "base rate"?I am using a 1 uS (or 1MHz) base rate.   Is
that fast enough?

I looked at the data sheet that comes with the lead shine drivers and
they all seem to require a pulse be high for at least 2.5 uS and then
low for another 2.5 uS.   This means the fastest possible period is 5
uS or 200KHz.

What I'm finding is that if I use a uP like an ARM-M i'm limited to
bout 1MHz base rate to go much faster I'll have to go with an FPGA and
then 10MHz is reasonable.

One more thing:  That 10% velocity jump represents a worst case rate
error of 5% but the average rate error  (I think?) be only 2.5% or 1/4
of the step size.

On Tue, Apr 3, 2018 at 7:46 PM, Jon Elson  wrote:
> On 04/02/2018 09:36 PM, Chris Albertson wrote:
>>
>>
>> How to generate pulses with 50nS jitter?  Use hardware, not software.
>> The uP has 10 hardware counter/compare timers built in and you can
>> program them to divide down the a 1MHz clock.
>
> If you have a 1 MHz clock, then you can't have any pulses with finer
> resolution than 1 us.
> So, a 100 KHz step pulse train will have an ~10% velocity jump to go to the
> next faster or slower velocity.
>
> My Universal Stepper Controller has a 10 MHz clock to the step generators,
> so that has 100 ns resolution.
> I recommend a 300 KHz maximum step rate with it, so the next higher or lower
> velocity is about a 3% jump.
>
> Jon
>
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Making a steper pulse generator, would like comments

[Jon Elson]

On 04/02/2018 09:36 PM, Chris Albertson wrote:


How to generate pulses with 50nS jitter?  Use hardware, 
not software.
The uP has 10 hardware counter/compare timers built in and 
you can

program them to divide down the a 1MHz clock.
If you have a 1 MHz clock, then you can't have any pulses 
with finer resolution than 1 us.
So, a 100 KHz step pulse train will have an ~10% velocity 
jump to go to the next faster or slower velocity.


My Universal Stepper Controller has a 10 MHz clock to the 
step generators, so that has 100 ns resolution.
I recommend a 300 KHz maximum step rate with it, so the next 
higher or lower velocity is about a 3% jump.


Jon

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Re: [Emc-users] What RPM

[Gene Heskett]

On Tuesday 03 April 2018 09:31:48 Marius Liebenberg wrote:

> There's a saying "It is not over until the fat lady sings"  now for us
> here it reads "It's not over until Andy has chipped in his bit". Just
> to keep us all on our toes and in line. Thanks Andy, very useful
> information and it just serves to make one feel confident from the
> start that you are not wasting your money on another failed attempt at
> building a special machine.
>
+1000. And I don't say it often enough myself. Thank you Andy.

[...]

> >My Rivett lathe is good for 1600rpm and has similar bearings. Your
> >bearings look smaller, and therefore can go faster.
> >
> >The internet says:
> >  "Depending on material max shaft speed 1.25 to 5m/s
> >(non leaded bronzes, up to approx 2.5m/s)"
> >
> >If the shaft is 25mm dia then 2.5m/s = 31 rps = 1900rpm.
> >
> >(the extremes give 950 to 3800 rpm.)
> >
> >--
> >atp
> >"A motorcycle is a bicycle with a pandemonium attachment and is
> >designed for the especial use of mechanical geniuses, daredevils and
> >lunatics."
> >— George Fitch, Atlanta Constitution Newspaper, 1916
>
> --
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> most engaging tech sites, Slashdot.org! http://sdm.link/slashdot
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-- 
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)
Genes Web page 

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Re: [Emc-users] What RPM

[Marius Liebenberg]

There's a saying "It is not over until the fat lady sings"  now for us 
here it reads "It's not over until Andy has chipped in his bit". Just to 
keep us all on our toes and in line. Thanks Andy, very useful 
information and it just serves to make one feel confident from the start 
that you are not wasting your money on another failed attempt at 
building a special machine.



-- Original Message --
From: "andy pugh" 
To: "Marius Liebenberg" ; "Enhanced Machine 
Controller (EMC)" 

Sent: 2018-04-02 21:44:36
Subject: Re: [Emc-users] What RPM

On 2 April 2018 at 15:23, Marius Liebenberg  
wrote:


 The spindle in the picture is what is currently fitted to the machine 
and I
 would like to refurbish and use it. The question I have is what RPM 
will I

 be able to run the spindle seeing that it uses these brass bearings?


My Rivett lathe is good for 1600rpm and has similar bearings. Your
bearings look smaller, and therefore can go faster.

The internet says:
 "Depending on material max shaft speed 1.25 to 5m/s
(non leaded bronzes, up to approx 2.5m/s)"

If the shaft is 25mm dia then 2.5m/s = 31 rps = 1900rpm.

(the extremes give 950 to 3800 rpm.)

--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916

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Re: [Emc-users] TSC, grrrrr.

[Gene Heskett]

On Tuesday 03 April 2018 00:40:27 Kurt Jacobson wrote:

> Gene,
>
> As far as I know ALL R8 collets have a 7/16"-20 UNF draw-bar thread,
> if it does not have that it is not an R8 collet!
> Your TSC does not stock UNF bolts? Pretty sure the ones around here
> stock both UNC and UNF in at least Grade 2.
> I know ACE stocks both UNF and UNC in Grade 2, 5 and 8 as well as in
> stainless, but we are lucky to have one of the better ACEs.
>
> While on the subject of thread standards ...
>
> I can't find it mentioned anywhere, but there is also what is
> sometimes referred to as a UNUF (Ultra Fine) thread.
> I guess it is not officially part of the UTS since I can't find a
> reference anywhere, but I have seen it referred to as UNUF on drawings
> and part lists. The "UNUF" I have encountered is 100tpi on small (#10
> and .25") set screws used for making fine adjustments on optical
> instruments and stages. You can get them from supply houses such as
> McMaster, so they are more or less standard parts.
>
I wasn't aware of those. Usually I've just made my own, but not finer 
than 50 tpi. But since putting tapered gibs in the 7x12, I think it 
could do 100 tpi stuff now. I haven't tried anything like that on the 
sheldon, but with hand sharpened HSS tooling I don't see why not. 
it did true up its own spindle by regrinding the short MT5 taper in its 
bore. Well enough an ER-40 adaptor runs at under .001 TIR 4" from the 
collet. And after the same grinder on the faceplates, the big chucks run 
pretty true.

And I'd like to cobble up a target to mount in the tailstock, and a laser 
diode in the spider so I could measure bed wear and calibrate that out 
with a lincurve/offset combo. The bed doesn't look that bad, but...  I 
didn't attempt to do tapered gibs when I rebuilt it, figured the 
carriage was heavy enough to hold it, but have since found thats not the 
case, I have seen it lift the 10 thou or so before the new gibs catch 
it.  Later this summer maybe. At the same time I put some preload in the 
z screw thrust bearing.  Despite some Reynolds wrap shims, it still has 
3 or 4 thou of end play.

> Cheers,
> Kurt
>
> On Mon, Apr 2, 2018 at 11:52 PM, Gene Heskett  
wrote:
> > On Monday 02 April 2018 21:33:22 David Berndt wrote:
> > > What? What exactly is the pitch/sizing on a USS bolt? Google
> > > doesn't really return much for a USS thread chart... UNS? 7/16-18?
> > > TSC was formed in 1938, perhaps you got their last piece of
> > > original stock?
> >
> > Their drawer marking is still old style, uss & sae. When they
> > actually label it that is.
> >
> > Eeecks!
> >
> > They changed the designation when I wasn't paying any attention, one
> > of the hazards of reaching my over-ripe age I guess.
> >
> > At  Nowadays
> > it appears what used to be USS is to be called by "UNC" (14 tpi for
> > a 7/16") and SAE is to be called "UNF" (20 tpi for a 7/16"). Ack
> > wikipedia, there is also a UNEF (28 tpi) but I've not seen one of
> > those critters in my 83 years plain enough to remember it.
> >
> > Its likely a good thing you called me on it, else I would have
> > carved a hunk of A2 to 18 tpi tomorrow.  And it still would not have
> > fit.
> >
> > But now I'm curious, do I have metric threaded R8's? The 14 screws
> > in a few degrees over a full turn before it jams. But the R8 is
> > Bridgeports pet tool holder so I assumed it was an American bolt.
> > And taking this one out of the G0704 is, shall we say, a "project"
> > thats is not going to happen unless it fails.  So I'd better get out
> > my taps and see how a 10mm coarse thread fits in one of these, I
> > might have a crossbreed of some sort. If you hear muttering from
> > North Central WV by the time the weather passes by tomorrow, you'll
> > know why.
> >
> > Thanks for the gentle reminder. I think you may have saved me from
> > making a mistake.
> >
> > > On Mon, 02 Apr 2018 19:35:27 -0400, Gene Heskett
> > > 
> > >
> > > wrote:
> > > > I rigged the 5C to ER-40 to the mills table, then found I needed
> > > > a draw bolt about 4" long to keep the R8 from rotating in the
> > > > ER40 collet.  So I saddled up and ran out to TSC, where I found
> > > > the 7/16 bolts they had were only grade 5.  So I got one and
> > > > some washers to adjust the length with, came back and found the
> > > > bolt was USS while the butt end of the R8 was SAE.  So I'll have
> > > > to round up some 1/2" A2 and put it all back in the lathe to
> > > > apply a g76 and make some SAE threads.
> > > >
> > > > I also found I'll  need a better way to clamp it to the table,
> > > > probably by making a big v-block and a thick steel bar to clamp
> > > > it into the V.
> > > >
> > > > Some days I swear its not worth gnawing thru the straps to get
> > > > up and pee in the mornings. :(
> >
> > --
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> >  soap,