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Modified OX CNC for Mitre Cutting (Picture Framing)

Discussion in 'CNC Mills/Routers' started by robbell, Jul 19, 2015.

  1. robbell

    robbell Well-Known
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    robbell published a new build:

    Read more about this build...
     
  2. Serge E.

    Serge E. Master
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    Interesting ... why not keep a 'normal' OX configuration with a narrow X (width of largest framing member to be cut), a short Y (basically enough to not only cut 45 degree angles, but also other angles for frames of 'odd' shapes) and let your framing piece to be cut in the Y direction with appropriate support if raw length is quite long (you are talking 3+ m !)

    Your g-code would then be to multipass angle cut. You could do 45 degrees but any other angle as well even curves and cutting tubing for some heavy duty frames ... or fancy joints (ex: to join a small tube over a larger one for later welding).
     
  3. robbell

    robbell Well-Known
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    Thanks for the input Serge.

    The X/Y axis in this still functions properly, it's just limited to operation within a small area of the whole board.

    Though your points to give me thought about making something along those lines.

    My main hurdle with this is how i hold the timber i'm cutting in-place, since it's not a flat sheet we're milling, it's just a thin (but long) length.
    Any thoughts on how i could achieve this?

    Programming in my current concept would also be very simple - it almost would never change.

    I'm working up a model based on your notes though, to have a closer look :D

    Thanks,
    Rob
     
  4. stargeezer

    stargeezer Veteran
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    I'm intrigued by the concept, since I'm involved with a woodworkers supply store that also supplies a lot of millwork. So if you don't mind, I'd like to pose a few pointed questions.

    1. Why have a Y axis at all - just use a single rail like a radial arm saw, with a pivot in the rear to allow a swing that is greater than your maximum cut angle. Place a lead screw parallel to the table that would move the rail to the desired angle.

    2. How wide is the widest material you will be cutting? Most frame shops I've been in only sale material in widths of less than 6" or 8" (150-200mm), so why build a machine with so much travel in the y (and x axis) axis?

    3. I don't recall reading if you are planning on using belts or lead screws, but I'd encourage you to use screws. I'm amazed that the belts work as well as they do on most applications, but screws offer endlessly repeatable positioning and just can't stretch.

    4. Why hang the machine overhead? It seems that it's going to be "in your face" :) why not under the table with the spindle and Z axis inverted so that it points "up" with the endmill sticking out of the table?

    Lastly, think out side the "box". You are flipping the "box" over, why not cut it up a bit. question why you need a box at all. :)

    I look forward to watching this progress.
    Larry
     
  5. Serge E.

    Serge E. Master
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    Could you do some sort of clamping system ... maybe hydraulic or just spring loaded with a foot control to 'pinch' the material being 'cut' by milling the angle ? You would need a reference edge to keep precision ...

    If doing just 45 degree cuts, you would need to 'flip' the material to minimise waste in your raw material, right? It is physically flipping the material or changing the 'cut' angle by 90 degrees ... depending on the profile of the material ? Making the machine CNC would 'flip' the angle precisely without flipping the material. Just slide it through to a stop

    If doing ONLY 45 degree cuts, you could probably mount a fix gantry (no Y !) at that permanent angle. X would be to cut/mill the width of your raw material while the Z would step down with each pass to actually do the cut. Instead of sawing the raw material with a blade (1/8" or possibly thinner) you would be milling the cut (probably 1/4" to reduce number of passes through the material). In this configuration, the Y would control the position of your 'stop'. Pinch rollers could move the material through the cutting area and fully automate the cutting process with a mechanism to remove the cut piece out of the way of the next cut ? Precision is possible ... it is a phlat cutter (origins of OX, no ?)

    With a wide enough 'clamp' you could probably get away with only two such clamps. One to hold the 'final' piece and second to old the 'scrap / left over' piece. Both clamps close enough to the 'cut' so they could have a fix position. The length of 'final' piece would be a factor. Otherwise, you will probably need four clamps which can be positioned as job requires. Hmm ... these clamps could either press the material down (or up) against a table or 'squeeze' the material - pushing it against a fixed reference edge. The latter would need to be 'open' near the cutting area... like a router table, miter saw, etc.

    I would not limit the machine to 45 degree cuts when it could easily do "any" angle, even curved cuts, with precision ... However, this would affect the configuration of the machine.

    Lots of potential here ...

    As a matter of fact, instead of moving a router/spindle into the material, this very specialized OX of yours could move a sawblade "slowly" up and down, especially if your cut angle is fixed... Nobody said the tool could not be a circular saw - properly mounted, of course.

    Would the saw blade last longer than the end mills ? Be as precise (like the 40,000 $ machines you mentioned) ?? It should be a quicker cut as it could do the entire width of your material ... just got rid of the X axis control, down to Z ... moving the blade down and up. The thicker the blade, the better the cut (no flexing) ??

    I'm just thinking out loud, here. It might spark a useful idea at your end ...

    If you really want to go specialized, you could basically end up with a CNC mitre saw and specialized software : Z would move the blade up and down, Y could change the angle (stepper controls one end, other is on a pivot) and X could add a sliding aspect for cuts as wide as your machine needs to cut. Go fancy and add a 4th axis to do compound cuts ! :rolleyes: It becomes just a matter of sliding the material through ... Your 'stop' could be a separate machine - just one axis : length.

    Are we looking at complicated solutions for doing repeat 45 degree cuts ? How many of these cuts are you planning to do anyways ?
     
  6. Serge E.

    Serge E. Master
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    The machine I'm alluding to would be capable of doing much more than picture frames ... think structural framing, cutting tubing (with proper 'clamps'), lumber, etc. So I might be the one looking too far ahead ... again, sorry.
     
  7. stargeezer

    stargeezer Veteran
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    As much as I'm all for building any machine within our abilities, for framing there's nothing more functional and durable (within the precision limits of the job being done) than the good old miter saw. I just can't see dragging a ox out to cut 2x4's.
     
  8. Serge E.

    Serge E. Master
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    Indeed. I was thinking more to do weird cuts such as needed to join tubing for structural framing. As for the 2x4s, a mitre saw can't do all needed cuts ... sometimes you need a circular saw (ex: stair stringer) or jigsaw / saws all (ex: cut out a notch of some sort). As you say, if not done in a production mode, the regular tools do a good enough job when needed. One pass with a blade of some sort is quicker than multiple passes with a bit.
     
  9. Joe Santarsiero

    Joe Santarsiero OB addict
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  10. robbell

    robbell Well-Known
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    Thanks for your reply. A few responses below.

    The main reason is accuracy and replication. My drop saw has a similar function with notches in it, but the accuracy isn't what it needs to be. Each time you move it, then move it back, it can be out by a fraction of a degree. Not an issue when building houses, but definitely when you're looking for the most perfect join.

    About 100mm deep is our max.
    The cutting bed is only 150mm deep between the rails.
    The travel in the machine is just a standard "kit" i can get in Australia. I'd likely trim these a little.

    I will likely change the machine to use screws (Z is a screw). Across a 3m span it's not possible so would probably go rack and pinion.

    The main reason is simplicity of the sub-structure.
    If i mounted it underneath i would need a large hole and space under the table for the machine.
    This way i can maintain a solid support structure.

    Again it's about simplicity really...
    Once it's all together and working i'm sure i'd see ways to re-engineer it in various ways, but for now i'm looking for a relatively fast / reliable build.

    Thanks,

    Rob
     
  11. robbell

    robbell Well-Known
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    My issue with clamping is that i need a foolproof and FAST way to clamp and ensure the cutter head isn't going to end up on top of it.
    That's what led to my design originally - a predictable clamping position / cutting path etc.

    That's the problem with making the support table the Y axis. If i have a predictable limit to the X/Y, then i can make sure all clamps etc are just outside that area for maximum support and zero risk.

    The programming can then be identical for every cut too - no need to feed measurements into it.
    I started drafting it last night based on your suggestion, but it created a few problems i'm unsure how to work out yet.


    This is a specific machine, and i don't really need it to do curved cuts etc. I just need great accuracy, and also the ability to compensate for just about anything (which is why i'm thinking CNC rather than fully manual machine). Theoretically i can just mount two mitre saws with a way to adjust them and get close to what i want too, but it's back to manual degrees of accuracy.

    Your final idea is one i've had too - but comes back to predictability. I need to be able to cut 1000 cuts with 0.01° or better precision.
    The better the cut, the neater the frames, the faster production.

    I hope that all makes sense?
    Rob
     
  12. robbell

    robbell Well-Known
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    For now, this is a specific machine :D So not thinking outside of picture framing for now.


    Yeah i would agree here. The mighty mitre saw is a great piece of equipment. I wouldn't use the CNC for anything not requiring the high precision such as what we need.

    Anything within about 1° would be fine for a house frame...



    Rob
     
  13. robbell

    robbell Well-Known
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  14. Serge E.

    Serge E. Master
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    You definitely want to automate and stay precise at those volumes ... the last has to be as good as the first.
     
  15. robbell

    robbell Well-Known
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    Yes - needs to be highly repeatable.

    Though all this discussion about options does make me think if simply two mounted / sliding mitre saws on rails which have a fine adjustment available would be a more viable / faster / cheaper / reliable option.

    As noted before, a high quality 10" blade is likely going to last longer than even the best spindle... and the cuts would be faster.

    Hmmmmm..

    Rob
     
  16. Serge E.

    Serge E. Master
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    One could be fixed - the reference saw, while the other - blade at 90 degree to first, slide to cut length. You could rig steppers to do both cuts at the same time (?) Twice as fast :thumbsup: The clamps could hold frame piece between the two saws. You would have a minimum length (distance between the saws) ...

    If you Can stack the raw material, each layer parallel to table ? You could then cut multiple lengths in one shot ... faster still ! You will be limited by the blades' diameter (minus hub and such).

    Maintenance making sure the saws are at 90 degrees to each other and the reference edge at 45 degrees to blades ...

    You basically want to end up with something like this :
    upload_2015-7-19_21-45-57.png

    (http://www.wwthayer.com/Window-Machinery-Atech-Double-Head-Miter-Saw-Norma-02-SA.asp) w/out the 16k$ (plus taxes, shipping, etc.) price tag !

    This one offers multiple angles and, apparently, more automation :
    upload_2015-7-19_21-48-39.png
    (http://www.hydrapower-intl.com/nc_miter_saw.asp)

    Lots of expensive industrial choices ...

    You should be able to build something less expensive for certain. Double rails for sliding one saw carriage on long length (you mentioned 3 m ?) If the saws can be less than 1000mm apart, maybe the C-beam can handle the saws and use a screw drive for positioning of the saw since you are looking for precision ...over speed. Definitely NEMA 23, if not bigger, to move the saw carriage as it will have some weight to it.

    Sounds like a fun useful project.
     
  17. Serge E.

    Serge E. Master
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    On what might be the low end of options (less than 5k$) and even portable (!) is the SawGear :



    (http://www.tigerstop.com/Products/SawGear.aspx)

    Hmmm ... kind of makes me wish I had a need to build one ... :rolleyes:
     
  18. stargeezer

    stargeezer Veteran
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    If I couldn't build that first saw for less than $5k, using much better parts, I'd eat the thing. $16k is such a total rip off!
     
  19. robbell

    robbell Well-Known
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    Yeah - all these machines are geared for "almost perfect"... we need just a fraction better than that.

    The length stop might have a resolution to 0.2mm, but the angles out of the mitre can still be off by 0.1°.

    I'm having a play with my mitre saw again to see how close i can get it using adjustments in the unit itself (screw bump-stops etc), to check feasibility of using two mitre-saws. Since each one can be individually adjusted it might prove more successful than what i've had previously. Else i'll just continue with my build.

    Rob
     
  20. robbell

    robbell Well-Known
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    Agreed :D
     
  21. Paruk

    Paruk Master
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    For a perfect miter every time…..use a table saw and a miter sled. Simple, reliable and easy to make. Jay Bates gives a good one here

    Further there are enough videos on the Tube to show you how. Look for Woodwhisperer, I Build it! and others. Some are even having very sophisticated miter sleds that can do repeatable cuts all the time.

    One time setup, and every time a perfect miter. I use them all the time for miters that have to be exact. Never use the chop saw for it.

    A good contractor saw (Boye is a brand they have in Oz, they are good and can be fine tuned to perfection easily) will cost you about US$ 600 to 700, the sled can be made out of scrap parts if you like.
     
    #21 Paruk, Jul 20, 2015
    Last edited: Jul 20, 2015
  22. stargeezer

    stargeezer Veteran
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    If you decide on the miter saw idea apart from finding saws that will mechanically give you the repeatability you need, you need to get the right blade too. If possible get saws that take a 12" blade. They are common here. Select a blade with the highest tooth count you can find and if possible a tooth angle that has as small a tooth angle as possible. 2.5 degree positive to 2.5 negative angle will give you the smoothest cut. Avoid aggressive tooth angle except for framing.

    BTW. This is also the best blade for cutting non ferris metals too, like aluminum v-slot. :)
     
  23. Paruk

    Paruk Master
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    For my miter saw I use 100 teeth blades. For miter or cross cuts a minimum of 60 teeth is required. Indeed, the 100 teeth gives a nice clean cut. But…as stated before (and many can confirm that) a miter saw is nice for the quick job in construction or for a building carpenter. For fine woodwork they are practically useless. I say, forget about a miter saw and go for a proper contractors saw or even a cabinet saw with a miter sled.. Your problem will be solved!
     
  24. Paruk

    Paruk Master
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    Nice video….but what do they show? A carpenter's job in a house. Nothing like fine woodworking, and that's what robbell is doing.
     
  25. stargeezer

    stargeezer Veteran
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    Years ago Bosch made a tool called the "Fine Cut Saw". My neighbor owns one. They are very much like a reciprocating saw with a very fine tooth, backed blade. His is hand held, but I seem to recall that they made them in a miter saw configuration too. It's been a long time since I was in the tool business but Perhaps they still make that or you may be able to find one used on ebay.
     
  26. Serge E.

    Serge E. Master
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    Did you notice how they use a plain old mitre saw, with all of its advantages and disadvantages (precision?) while claiming precision cuts thanks to their "automatic" stop to set cut length ? The angle can still be off !

    It was to show a 'model' of what was mentioned by Robbell himself as he explored solutions and building a machine for his needs. It brings out the need to adjust calculations for the angle, etc. not just straight cuts.
     
  27. stargeezer

    stargeezer Veteran
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    The problem with sliding compound miter saws is exactly precision, just as Serge quotes from the video. the more movements a saw has, the more slop it is going to have - which will only get worse with time and use. Contractors get by with this because a. their cuts really don't need fraction of a degree accuracy, b. they use their saws hours a day and build muscle memory that makes minute physical adjustments to offset the slop they will have, and c. it's a piece of framing wood they are cutting and a hour after the cut the shape/size of the wood will change by an amazing amount. That's why they nail it in place as fast as it's cut.

    When I was selling tools we would ask the customer what they were going to use the saw for and try to sell them the right one for the job. The customer would not always take our advice and then we'd see them again in 6 months when they got tired of fighting with the "wrong" tool.

    Were I selling one to the OP I'd suggest, Cast iron base, 12" blade minimum 14" would be better but harder to find and more expensive, movements in ONLY two directions - cut and angle. I'd select a saw that had real bearings in the spine - not bushings that would wear out quicker and it would be the saw that had the beefiest cast iron backbone and hinge I could find. A industrial saw - not a consumer/contractor grade saw. I'd also make sure it had a closed frame type of motor on it, not the cheap induction motors that are sold bragging that they are 5hp but fit in a coffee cup. I would not be surprised that it would cost more than $1k perhaps as much as $2k, but it would be worth every penny if you are making your income with it, and the only things you'd ever need to change would be the blade, someday the switch and perhaps the drive belt. You'd pass this saw down to your kids perhaps grandkids.
     
    #27 stargeezer, Jul 20, 2015
    Last edited: Jul 20, 2015
  28. stargeezer

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