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Re: [taigtools] Re: hard to retrofit taig lathe for CNC? To powerfeed or not powerfeed

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  • Tony Jeffree
    Juan - Unfortunately, there is a fundamental flaw in your starting point - your use of a triangular tooth-form for your rack . So no, what you have in your
    Message 1 of 53 , Feb 1, 2012
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      Juan -

      Unfortunately, there is a fundamental flaw in your starting point - your
      use of a triangular tooth-form for your "rack". So no, what you have in
      your vids, and what you have described in your posts here, certainly
      doesn't "recapitulate (my) webpage", and it looks like you really haven't
      understood the geometry.

      The tooth form of an involute rack isn't triangular; it is (as shown in the
      figures on my webpage) trapezoidal. If you use a triangular "rack" tooth
      form to try and generate an involute gear, the result will be that the
      teeth end up too thin and consequently the gaps between them too wide. If
      you limit the "generation" technique to just one cut per tooth, as you say
      you do, the result is a very strange tooth form indeed - just for
      amusement, I used my drawing of Figure 1 on my webpage as a starting point,
      and adjusted the "rack" cutter to have triangular teeth, and the result
      after a half dozen passes can be seen here:

      http://f1.grp.yahoofs.com/v1/YEUpT56kTVIitVbZu7PwbNlaYv-UHbWDvoDPf41OhhdZsdGvy_589tZLJYO1_bzJ_KANMhWrH7zVUBP3dhiV5Ho4b9vm96lxCw/Tony%20Jeffree%27s%20Files/Gear%20cut%20with%20triangular%20rack.pdf

      My guess is that, if you are managing to make gears that actually mesh, you
      are compensating for this thin tooth effect by decreasing your depth of cut
      to compensate for the fact that you are using the wrong shape of cutter.

      Regards,
      Tony



      On 1 February 2012 05:30, juangelt <juangelt@...> wrote:

      > Tony, my vids recapitulate your webpage.
      > there is no misunderstanding or disagreement.
      > you expressed the geometric principles in html.
      > i did it with avi.
      > if it wasn't pitched to your level, so be it.
      > but get this straight-
      > there is no 'if i read your webpage, NOW i understand' stuff.
      > you didn't educate me. i made all the effort on my own. i bought the book,
      > i studied the geomoetry, i wrote the software to make the cutter to make
      > the gear. i made the vid to show it.
      > i appreciate the understanding that you show in your html. it's exactly
      > what i understand. it's also what i said in plain english in my posts here
      > and in a set of videos that demonstrate it ain't purely academic.
      > do you actually get away with talking to people like that in real life?
      > it's not acceptable in my community but what's it to me if you learn
      > manners or not? go ahead and piss on your forum. it's your forum. you live
      > in it. i don't have to.
      > but yeah - lucky me, i preserve the capacity to judge b.s. and i don't
      > care if anybody doesn't like it. it's a perq of being batso.
      >
      >
      >
      >
      > --- In taigtools@yahoogroups.com, Tony Jeffree <tony@...> wrote:
      > >
      > > If you read my page, then you should now understand (a) that doing one
      > cut
      > > per tooth position results in a lousy tooth form, and (b) that having
      > more
      > > than 3 teeth on the cutter doesn't help you get the tooth form any
      > better.
      > > The only thing that helps is to increase the number of cuts you take, and
      > > move the cutter. If you haven't understood that, I would respectfully
      > > suggest that you read it & study the diagrams again.
      > >
      > > And yes, I get the whole cheap video technology thing, but as your videos
      > > demonstrate quite clearly, it's very hard to use them in such a way that
      > > they give a clear picture of what is actually happening.
      > >
      > > Regards,
      > > Tony
      > >
      > >
      > >
      > > On 31 January 2012 21:54, juangelt <juangelt@...> wrote:
      > >
      > > >
      > > >
      > > >
      > > > i read your page on the subject. i know you get the geometry.
      > > > the reason i don't need to make but one pass per tooth is that i make
      > > > cutter with many teeth and in the video it shows how many are engaged
      > with
      > > > the blank. i can observe the wear on the cutter as proof that no fewer
      > than
      > > > 8 teeth were engaged with the blank, implying that at least 8 facets
      > are
      > > > cut on each side of each tooth.
      > > > fancier code could indeed move the cutter as the blank rotates to get
      > as
      > > > perfect an involute as the machinery is capable of resolving.
      > > > how much machine time is a gear worth for the purpose?
      > > > the sensible way is to cast the suckers, imo...lol
      > > >
      > > > i used to do html like your page but since cheap cameras arrived i make
      > > > videos.
      > > >
      > http://www.youtube.com/user/BrainWeather?feature=mhee#p/c/3413C9F854491F81
      > > >
      > > >
      > > >
      > > > --- In taigtools@yahoogroups.com, Tony Jeffree <tony@> wrote:
      > > > >
      > > > > You are correct that a rack-form cutter can be used to cut gears of
      > any
      > > > > number of teeth, but as I demonstrated to my own satisfaction (&
      > wrote up
      > > > > in the article that I posted -
      > > > > http://www.jeffree.co.uk/pages/multi-tooth-gear-cutter.htm), you
      > need to
      > > > > make more than one pass per tooth if you want anything better than a
      > > > crude
      > > > > approximation to the correct involute tooth form, because in reality,
      > > > > although it seems like the multi-tooth rack-form cutter is helping
      > form
      > > > the
      > > > > involute, only 3 of the teeth of the cutter actually do any useful
      > > > cutting
      > > > > work (see the drawings & explanation in the article). Yes, in Figure
      > 1,
      > > > the
      > > > > outer two cutter teeth of a 5-tooth cutter do take a small nick out
      > of
      > > > the
      > > > > blank, but that nick doesn't contribute to the final tooth form at
      > all -
      > > > > eventually, that nick is totally erased by a subsequent, larger cut
      > made
      > > > by
      > > > > one of the middle 3 teeth of the cutter. If you don't believe me, do
      > > > what I
      > > > > did and draw it out carefully on a CAD system & see exactly what
      > happens
      > > > as
      > > > > you rotate the blank by full tooth spaces, then compare with what
      > happens
      > > > > when you rotate fractions of a tooth between cuts and also move the
      > > > cutter
      > > > > a corresponding distance in the direction of rotation - as if the
      > rack is
      > > > > engaged with the embryonic gear. The difference in the accuracy of
      > the
      > > > > tooth form is quite dramatic - four passes per tooth, rotating the
      > blank
      > > > > 1/4 of a tooth (and advancing the cutter by 1/4 of a tooth width)
      > between
      > > > > passes gives a much better tooth form, pretty close to the ideal
      > > > involute.
      > > > > And actually, using that technique, a single tooth cutter works just
      > fine
      > > > > too, which is good news because it is a lot quicker to make.
      > > > >
      > > > > Regards,
      > > > > Tony
      > > > >
      > > > >
      > > > >
      > > > > On 31 January 2012 20:34, juangelt <juangelt@> wrote:
      > > > >
      > > > > >
      > > > > > might be worth noting that the cutter with triangular teeth shown
      > in
      > > > the
      > > > > > vid that is used with the procedure i described will cut a gear of
      > the
      > > > > > designed pitch with any number of teeth whatsoever because it has
      > more
      > > > than
      > > > > > one tooth and is cutting many teeth at once at various angles which
      > > > define
      > > > > > the involute form.
      > > > > > might not be worth noting, too... all a matter of what it gets
      > me, eh?
      > > > > > already i'm sorry for the bother.
      > > > > >
      > > > > > --- In taigtools@yahoogroups.com, "juangelt" <juangelt@> wrote:
      > > > > > >
      > > > > > > ok, my bad for language abuse - saying 'triangular' instead of
      > > > 'straight
      > > > > > sided'. i didn't mean to invite dispute.
      > > > > > >
      > > > > > > now, if someone wants to make a cutter following the recipe i
      > > > described,
      > > > > > it will be found practical to extend those lines to the apex and
      > hope
      > > > that
      > > > > > it stays sharp enough thru the cutting job to keep a root deep
      > enough
      > > > that
      > > > > > it doesn't cause interference. that was a suggestion i got from the
      > > > book on
      > > > > > gear cutting i bought so i could learn the principles involved.
      > > > > > > i only get about 250 teeth in 1/4 brass with a home.brew cutter
      > > > before
      > > > > > it's quite dull, even though i case harden it as the collection of
      > > > videos
      > > > > > on the subject show.
      > > > > > > in any case, it's fortunate that all the software i wrote to
      > generate
      > > > > > the code to make the cutter to make a spur gear that works very
      > nicely
      > > > > > wasn't the result of pure stupid luck. the videos would have been
      > > > seriously
      > > > > > nasty if they misinformed people, too. i'm glad i don't have to
      > remove
      > > > > > them. sometimes i get it right even if it's pure dumb luck.
      > > > > > > the only people who make fewer than 2 mistakes are the ones who
      > never
      > > > > > try to do anything at all...lol
      > > > > > >
      > > > > > > --- In taigtools@yahoogroups.com, Tony Jeffree <tony@> wrote:
      > > > > > > >
      > > > > > > > Ron -
      > > > > > > >
      > > > > > > > The commercial gear cutters are, as you observe, a compromise,
      > as
      > > > they
      > > > > > are
      > > > > > > > each intended to cut a range of tooth counts. Strictly
      > speaking, a
      > > > true
      > > > > > > > rack cutter should have straight flanks and would cut a rack
      > with
      > > > > > > > (similarly) straight flanks - and this is of course the right
      > > > > > (involute)
      > > > > > > > tooth form for a gear with an infinite tooth count (a rack).
      > > > > > > >
      > > > > > > > You can generate the right involute tooth form for any tooth
      > count
      > > > if
      > > > > > you
      > > > > > > > start with a rack-form (straight flanked) cutter, and have
      > suitable
      > > > > > amounts
      > > > > > > > of patience, as I described in this article:
      > > > > > > >
      > > > > > > > http://www.jeffree.co.uk/pages/multi-tooth-gear-cutter.htm
      > > > > > > >
      > > > > > > > Regards,
      > > > > > > > Tony
      > > > > > > >
      > > > > > > >
      > > > > > > >
      > > > > > > > On 31 January 2012 18:23, Ron Thompson <ron@> wrote:
      > > > > > > >
      > > > > > > > > On 1/31/2012 1:02 PM, Ron Thompson wrote:
      > > > > > > > > > > i'm prepared to be corrected and educated.
      > > > > > > > > > > here's one source of the information i used
      > > > > > > > >
      > > > > > > > > I think I see our difference of opinion. The book you cite
      > keeps
      > > > > > talking
      > > > > > > > > about a rack having straight sides. What you said was
      > > > triangular. Not
      > > > > > > > > the same thing.
      > > > > > > > > An involute form changes for the number of teeth. At
      > infinite, or
      > > > > > rack,
      > > > > > > > > it is indistinguishable from straight sided.
      > > > > > > > > Since the commercial cutter for a rack also cuts some number
      > of
      > > > > > gears,
      > > > > > > > > it is involute.
      > > > > > > > > This is what I was taught in machinist school.
      > > > > > > > >
      > > > > > > > > --
      > > > > > > > >
      > > > > > > > >
      > > > > > > > > Ron Thompson
      > > > > > > > > On the Beautiful Florida Space Coast, right beside the
      > Kennedy
      > > > Space
      > > > > > > > > Center, USA
      > > > > > > > >
      > > > > > > > > Think, Draw, Print. 3D printers ROCK!
      > > > > > > > >
      > > > > > > > >
      > http://www.plansandprojects.com/My%20Machines/PrusaMendel2012-1/
      > > > > > > > >
      > > > > > > > > http://www.plansandprojects.com My hobby pages are here:
      > > > > > > > > http://www.plansandprojects.com/My%20Machines/
      > > > > > > > >
      > > > > > > > > Visit the castinghobby FAQ:
      > > > > > > > > http://castinghobbyfaq.bareboogerhost.com/
      > > > > > > > >
      > > > > > > > >
      > > > > > > > >
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      > > > > > > > >
      > > > > > > > >
      > > > > > > > >
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    • alighazizadeh
      Hi, The side lead screw is the best that you can do with the little taig as the base is filled with concrete. Many larger lathes also have this on the side
      Message 53 of 53 , Feb 5, 2012
      • 0 Attachment
        Hi,
        The side lead screw is the best that you can do with the little taig as the base is filled with concrete. Many larger lathes also have this on the side without any apparent problems.

        Regards,

        A.G



        From: baboonhead11
        Sent: Sunday, February 05, 2012 8:40 AM
        To: taigtools@yahoogroups.com
        Subject: [taigtools] Re: hard to retrofit taig lathe for CNC? To powerfeed or not powerfeed



        I've finally gotten the whole rig setup and even turned a little piece for testing.

        I gotta say, the rack and pinion is terrible. backlash is quite significant, although from a purely manual perspective it doesnt really matter as long as you have dials everywhere and measuring actual movement. However the z resolution isnt as great I suppose.

        Im definately going to add some sort of leadscrew to my setup and take out the geared handle.

        This leads me to a followup question. From the few CNC retrofits and powerfeed version that I have seen, they seem to put the leadscrew on the front side of the lathe, near where the rack and pinion resides.

        With regards to this, isnt this setup not as ideal, given that any leadscrew will be further off-center from the tool-holder bed? In the ideal world, the leadscrew should be centered along the center of the stage so that you dont get excessive friction at opposite corners of the dovetails of the bed, given that there is always going to be some gap spacing on the dovetails?

        --- In taigtools@yahoogroups.com, Tony Jeffree <tony@...> wrote:
        >
        > I haven't tried the g-code output features yet, so I can't comment on that.
        > As you say, a fun program though!
        >
        > Regards,
        > Tony
        >
        >
        >
        > On 3 February 2012 11:52, alighazizadeh <alighazizadeh@...> wrote:
        >
        > > Hi Tony,
        > > I have down loaded the trial version of the software you mention and it
        > > indeed does have the limitation that you mention so for small scale gear
        > > cutting it is hopeless and it also doesn't seem to generate any code on my
        > > computer perhaps due to it being a trial version but it is fun to generate
        > > data as you mention.
        > >
        > > regards,
        > >
        > > A.G
        > >
        > >
        > > From: Tony Jeffree
        > > Sent: Friday, February 03, 2012 7:36 AM
        > > To: taigtools@yahoogroups.com
        > > Subject: Re: [taigtools] Re: hard to retrofit taig lathe for CNC? To
        > > powerfeed or not powerfeed
        > >
        > >
        > >
        > > Ken -
        > >
        > > Art Fenerty (of Mach 3 fame) has developed a package called "Gearotic" (
        > > http://gearotic.com/ ) that can generate the necessary G-code to cut
        > > involute spur gears using an end mill. The only constraint is that the end
        > > mill needs to be no larger than the space between adjacent teeth, so that
        > > tends to limit the technique to cutting gears with a large module size.
        > >
        > > It is a fun package to play with because it can sim arrangements of
        > > multiple gears & also draw out non-circular gears and (more recently) clock
        > > escapements too.
        > >
        > > Regards,
        > > Tony
        > >
        > > On 2 February 2012 21:05, Ken Cline <cline@...> wrote:
        > >
        > > > On Feb 2, 2012, at 9:23 AM, juangelt wrote:
        > > >
        > > > > therefore, a cutter with TRAPEZOIDAL teeth can cut any size gear of
        > > that
        > > > pitch at any resolution one desires - something i find really wonderful.
        > > >
        > > >
        > > > Of course you can also cut gear teeth with a plain old end mill. I make
        > > > credible approximate-involute gears this way, sweeping the end mill
        > > across
        > > > the face of each tooth several times to cut facets. Using a ball end
        > > > cutter leaves nice bottomland fillets that eliminate stress concentrating
        > > > angles at the base of the teeth. I have designed and used this technique
        > > > to make custom gears that mesh at multiple pressure angles (e.g. mating
        > > > with two gears of the same overall size but differing number of teeth).
        > > >
        > > > It is worth mentioning that these approximate-involute approaches tend to
        > > > leave a little extra material n the gear teeth, getting closer and closer
        > > > to the true involute form as more facets are cut. Gears made to this
        > > shape
        > > > will therefore interfere with each other, and therefore won't mesh at
        > > they
        > > > true pitch radii. Widening the rack-cutter's teeth, changing its angle,
        > > > its position when cutting, or a combination of these techniques will
        > > > produce gears that mesh at the design distance.
        > > >
        > > > Compare this to the standard numbered involute gear cutter approach: Each
        > > > numbered cutter produces a smooth involute shaped profile, which never
        > > has
        > > > extra material on the tooth so that the gears produced never interfere
        > > when
        > > > run at their pitch radii. The deviation from ideal shape arising from
        > > > using a small number of cutters to produce al gears is not usually a
        > > > problem because the involute shape allows the gears to still mesh at
        > > > constant pitch angle and angular velocity ratio, albeit with a small
        > > amount
        > > > of backlash (and small change in pitch angle).
        > > >
        > > > By the way, we have examples of complex mechanical gearing at least two
        > > > thousand years old (e.g. the Antikythera Mechanism). Hand cut gears with
        > > > crudely controlled profiles proved serviceable in ancient times. Involute
        > > > gears were first proposed by Leonhard Euler in the 1700's.
        > > >
        > > >
        > > >
        > > >
        > > > [Non-text portions of this message have been removed]
        > > >
        > > >
        > > >
        > > > ------------------------------------
        > > >
        > > > To Post a message, send it to:
        > > > taigtools@yahoogroups.com
        > > >
        > > > To Unsubscribe, send a blank message to:
        > > > taigtools-unsubscribe@yahoogroups.com
        > > >
        > > > Let the chips fly!
        > > > Yahoo! Groups Links
        > > >
        > > >
        > > >
        > > >
        > >
        > > [Non-text portions of this message have been removed]
        > >
        > >
        > >
        > >
        > >
        > > [Non-text portions of this message have been removed]
        > >
        > >
        > >
        > > ------------------------------------
        > >
        > > To Post a message, send it to:
        > > taigtools@yahoogroups.com
        > >
        > > To Unsubscribe, send a blank message to:
        > > taigtools-unsubscribe@yahoogroups.com
        > >
        > > Let the chips fly!
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        > >
        > >
        > >
        > >
        >
        >
        > [Non-text portions of this message have been removed]
        >





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