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  1. #41
    Ger21 was right about the acceleration. 0.2g would be good.
    Just spotted I was putting 12A into my 4A motors!

    ^Am I right(that I was wrong!). What sort of current should I put in 'Set phase current' box?


    It was all seeming too simple, both options were more than adequate. Now I'm down to much lower accelerations, and that's still with the optimistic flat torque model.

    I've taken advantage of higher ball screw efficiency, and better value for screw inertia.

    I need to program some realistic cutting operations to see if I can spot any difference between the machine options.
    Attached Files Attached Files

  2. #42
    Quote Originally Posted by jimbo_cnc View Post
    Ger21 was right about the acceleration. 0.2g would be good.
    Why would you doubt some one with Gerry's experience or any of the Very experienced members here like Jonathan or me.? Also if you look again he's saying IF you achieve 0.2G.? It's not clear cut or an exact science in practise with so many outside variables playing there part.

    None of Us will deliberately send you wrong, We have no reason or motivation to do so unlike some of the Machine providers but you seem very distrusting and If I'm honest I for one, having bent over backwards offering sound advice to help find it quite insulting.!

    I don't understand why your not believing what's being told to you.?
    Last edited by JAZZCNC; 10-03-2015 at 10:07 PM.

  3. #43
    Having to explain a simple acknowledgement is tiresome, but here goes:

    Ger21 implied that I might not achieve 0.2g because the torque might only be 25% of the static torque. That didn't concur with the spreadsheet (gleaned from a presumably respected member), many posts about corner speed I've seen, or the the torque curves I found when searching. I also know Ger21 deals with high performance machines so it seemed plausible to me that he is used to dealing with a different part of the torque curve, so he might have rules of thumb that don't apply to my low speed machine.


    If you want to feel insulted go ahead, but don't take offense on behalf of other people.

    And you are overestimating how helpful you are being. What exactly are you telling me, apart from 'In my expert opinion, that's no good'. All I see is rants against chinese machines, with nothing to back it up (Why does that driver 'just about cut it' ? still waiting for that 'help'). And no suggestions (or offer) of alternative machines.


    I think it's clear we have a different approach. I'm not interested in trusting or not your experienced guesses about what will work, I want data and a model that I can use to find the quantitive answers myself and do comparative analysis.

    I wouldn't doubt anything Jonathan said, as I know from what I've seen on the forum before that he'd have the maths and data to back it up.

  4. #44
    Quote Originally Posted by jimbo_cnc View Post
    If you want to feel insulted go ahead, but don't take offense on behalf of other people.
    Did I say anything about insulting other people.!!
    " and If I'm honest I for one, having bent over backwards offering sound advice to help find it quite insulting.!"

    Quote Originally Posted by jimbo_cnc View Post
    All I see is rants against chinese machines, with nothing to back it up (Why does that driver 'just about cut it' ? still waiting for that 'help'). And no suggestions (or offer) of alternative machines.
    No rants about chinese machines I've always been clear about them.!! They have there place, which is learning, but they are cheap for a reason and that is they use Cheap electronics with cheap components poorly and weakly built. Which means they leave a lot to be desired in actual use. Yes IMO they are Crap.!

    Like wise the the Machine you where or are looking at was all mixed up with regards to spec. ie 32mm ballscrews with 3500mm/min rapids. I Told you this on the phone and explained why in some detail.
    I also told you I had nothing against Cheap Chinese Manufacturers other than they build to price so something has to give and often IME that is electronics and build quality. I also told you this was learnt from experience upgrading or fixing others machines not just my opinion.

    Also just for Clarity for those who know I build machines so may be thinking I told you this to put you off so I could build you one.!!
    I was also very clear from the start that I was only telling you this information to help you because I couldn't build you one even if you wanted me to.

    Now if offering my phone number and taking time out fo my day isn't helpful then what is.!!

    Regards not offering an alternative machines then it's quite simple why.? I didn't because there isn't any company I know in UK or Europe that Could (Or would supply that spec) at that size for $4000 you where being quoted.!! . . . This alone should say something to you.!

    Regards me not offering an explination or helping to why those drives are only just cutting the mustard for 6Nm nema 34 motors so worse for larger motors then why the hell would I waste time or offer my hard learnt experience to some arrogant person who doesn't listen.!! . . . . It will be a cold day in hell before I offer any more advise to you sir.

    Good Luck.!
    Last edited by JAZZCNC; 11-03-2015 at 01:31 PM.

  5. #45
    The fact is I do listen. Since you said 32mm was too big I've spent a week investigating and learning about machine design. It turns out that 32mm is probably fine, but I will most likely go for the slower speed, higher acceleration 25mm option.

    If you tried reading a post now and then instead of flying off on a rant, you would know it's not a 3500rpm machine with 32mm ballscrew.

    And once again you throw up barriers that don't exist. I'm not asking for a $4000 machine. I'm looking for best overall value that meets my needs. And that's lifecycle costing, so it includes resale value.

    When I add taxes and shipping the machine I'm looking at is about $6000. On paper it meets my needs. So if there was a machine going for $8000 that I thought was a bit betterr, or that I could get sooner, I'd snap it up. A $10k machine would have to be considerably better. As it is I'm happy to go with the best option I've found so far and take the risk that eg the electronics might need upgrading if your predictions come true.

    I appreciate you are trying to be helpful, but once you've given out some advice you have to let it go, you can't dictate what I do with that advice.

  6. #46
    Quote Originally Posted by jimbo_cnc View Post
    If you tried reading a post now and then instead of flying off on a rant, you would know it's not a 3500rpm machine with 32mm ballscrew.

    And once again you throw up barriers that don't exist. I'm not asking for a $4000 machine. I'm looking for best overall value that meets my needs. And that's lifecycle costing, so it includes resale value.
    Last word that will come from ME just to clear your twisting words.!

    My advice was given based on the conversasion on the phone where you was quoteing 32mm screws and 3500mm/min feeds amongst other things.
    Advice was 32mm screws are too large and not required. Also 3500/mm/min Max cutting feed was too slow for correctly cutting the materials you planned.
    Which you clearly didn't believe or want to hear hence this thread and when other very experienced people confirmed you still didn't believe. Hell only a few post's back you had the arrogance to tell probably THE most experienced DIY and Professional Users on the Net (Gerry) that he was wrong and Torque only dropped after the speed curve.!!

    Now I don't give a flying F'#K what you do with any advise I give but I do take execption when you try to make out I'm wrong and try to twist facts/words to show me in a bad light.!

    Oh and The $4000 came from you and the quote given not me and you where chasing price from the start because you considered building it your self which you asked me for ballpark figure of components.!

    Now Jog on and I'll watch for your RFQ in 12 or so months time.!!
    Last edited by JAZZCNC; 11-03-2015 at 03:54 PM.

  7. #47
    You picked some numbers I've said and joined them together to make a machine/requirement that doesn't exist. As you won't allow me to correct you, there's not much I can do about that. Rant on my friend.

    You clearly do give a fuck what I do with the advice.

    I didn't tell Ger21 he was wrong.

  8. #48
    You most certainly implied that Ger21 was wrong IN YOUR POST no 35. G.

  9. #49
    I have already mostly explained this, but let me expand.

    first, post 33, which is what I though Jazz was on about.

    When I say "As I understand it, I'm below corner speed even at max feedrate, so I have full torque available." That's a qualified statement, "As I understand it" means just that, but it also implies a lack of certainty. That lack of certainty is because it's not my domain of expertise and I'm questioning what someone else is saying.

    When it's in my domain of expertise and I'm confident I will just state outright "This is how it is"


    Post 35.

    I can see how you might read that as me saying Ger21 is wrong. But try this for size: It's a link to a document that says something, and below it is a summary of what that page says. It's not me saying that.

    I suppose it comes down to attitude, if you want to see that as me telling Ger21 he is wrong, go ahead. You could instead choose to see it as me probing for the correct answer, with proof.

    I'm not sure what else I could have done. Someone on a forum, who I know nothing about, states something contrary to all the previous information I've seen. What would you do? just accept it?


    I suspect Ger21 understands all this, maybe he's had to explain to lots of people that corner speed is not normally applicable (or whatever the answer is, I still haven't got to the bottom of this one). Or maybe he just works in an environment where asking for evidence is not taken as a personal insult.
    Last edited by jimbo_cnc; 12-03-2015 at 04:09 PM. Reason: removed trailing words that shouldn't have been there.

  10. #50
    I haven't received my torque curve yet!

    But in the meantime I've done some more thinking about acceleration and realised that torque fall off with speed is not a big problem anyway, at least for cutting profiles on wood. For the design case mentioned elsewhere of maintaining feedrate on curves, the acceleration is out of phase with the velocity, which helps a lot.

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