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Ideas to increase Z-axis cutting height in the Workbee cnc ?

Discussion in 'Concepts and Ideas' started by Exodon, Oct 3, 2018.

  1. Exodon

    Exodon Well-Known
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    Hi Community

    Based on the workbee kit ( from ozznest or openbuilds), I'm looking for ideas to increase the Z-axis cut depth and after reading some section of the forum I found two solutions.

    One is shared on a nice build done here: https://openbuilds.com/builds/workbee-cnc-build-my-honest-opinion-tips-and-help.6407

    [​IMG]

    Other options that I found is add a taller plates like this ones :
    WorkBee CNC 1" Taller Deluxe Y Side plates (seen at Openbuilds) | eBay

    "In addition to giving 1" / ( 25,4 mm) more Z travel " based on the description.

    So please in case someone have extra ideas will be great to see them.

    My objective is to reach the minimum of 6 to 8cm depth + the waste board. Im going to work with pieces longer then the machine, something like :
    [​IMG]

    workbee-z-height.png

    However I want to keep the rigidity of the machine without changing so much the kit...adding the taller plates looks the more logic, however I'm open to suggestions.

    Thank you all

    Regards
    Ricardo
     
    #1 Exodon, Oct 3, 2018
    Last edited: Oct 3, 2018
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Based on using the US version of the Workbee 1010 which has about 86mm clearance in the stock build all you would really need to do is turn the Z-axis around, fixing the Z-axis C-beam to the X-axis gantry plate and mounting the router mount to the Z-axis plate which will now run up and down on the fixed Z-axis rail. You will probably also need to trim the bearing plate at the bottom of the axis to where the router will clear. Reference file attached.

    Workbee Z reversed.jpg

    If you were wanting to go with the US version of the 1510, merely build the base low profile similar to the 1010 and go with the reversed Z-axis suggestion above.
     

    Attached Files:

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  3. Exodon

    Exodon Well-Known
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    Hi Rick
    Thank you for the tip, this is a interesting approach! You did this to your machine ? Soon I have the machine going to simulate this approach....
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Not yet but I'm considering modding my Ox to include it. The idea has been floating around the forum for quite some time regarding the best way to increase working depth. (One previous thread here.) While the method has its limitations it is a far better approach as it induces less leverage on the system than jacking the X-axis up and then having to reach back down to the work piece. Less leverage means less overall flex in the system and more accurate cuts.

    The only other suggestion I would offer would be to add a second spindle mounting ring just below the plastic spindle top to help stabilize the router. I'm not really a big fan of extending the router that far down in the mount but in your case it is necessary to achieve the depth required.
     
  5. Exodon

    Exodon Well-Known
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    Hi Rick
    Very interesting topic there...In end of the discussion I understand the pros and cons of both solutions. To be honest if the spindle is well blocked with a improved plate might be better compare to the flexible z-axis move. I might try this when I get the machine....
     
  6. Metalguru

    Metalguru Master
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    Just take off the spoil board. That would give you another almost 60mm of travel. Your work would have to fit between the supports, and you may have to extend the Z axis C-Beam to 300mm instead of 250...

    MG
     
    #6 Metalguru, Nov 2, 2018
    Last edited: Nov 2, 2018
  7. Metalguru

    Metalguru Master
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    Rick:

    It's easy to add a second router mount to the Z axis to stiffen things up, particularly when you have a router with a long body like the Dewalt or the Makita. You may not be able to put all 4 angle brackets on the second mount because of space limitations, but the router body ties them together pretty well.

    I took a second look at your modification for the Z axis, and I'm not sure how that would give any significant increase in travel? The router mount plate still only moves the same amount either way... About the length of the C-beam - the length of the plate. How is this any different from the original? I do see where you could adjust the Z axis position by moving the c-beam up and down, but you'd have to disassemble the whole X axis to make this adjustment...

    MG
     
  8. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    MG,

    The issue is the extension of the bit below the bottom axis plate. With a fixed spindle on a moving axis, if you have say 3" clear beneath the bottom axis plate but the extension of the bit is fixed 1 1/2" below the plate you really only have 1 1/2" of working depth (motion) remaining. On a fixed axis/moving spindle system, the bit can be fully retracted above the bottom of the lower axis plate to where you can effectively use the full 3". Obviously there are limitations to this, mainly that you can't cut any deeper than the length of the bit. But if you're cutting 3" foam with a 3" bit you can get away with having only a 3" throat on a moving spindle system. On a moving axis system this jumps to 6" due to the loss from the fixed bit extending into the throat.
     
  9. Metalguru

    Metalguru Master
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    I'm still not getting how this improves anything. Since, in either case, your cutting depth is limited to the length of the bit, that's as deep as you can go, period. Reversing the Axis to the "moving spindle" configuration gains you some height for the work underneath the Z axis but you still only get the length of the bit for effective travel.

    The way you have it shown in the model above, I doubt that most bits would even be able to reach the table to make through cuts. I've never seen a 3" long 1/4" router bit, they may exist but they are going to be very expensive, and very fragile. I suppose you can change the mounting height of the router, but this only changes the absolute height, not the travel.

    Also, there are no holes on the Workbee front X axis plate that line up with a c-beam for mounting purposes, so you would have to modify or make a new plate to do this modification. This is another reason that I advocate using the C-Beam XL plates for the Workbee X/Z axis, it makes it so much easier to modify things, and the loss of one pair of wheels on the top makes little difference in rigidity.

    MG
     
  10. Giarc

    Giarc Master
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    Kodiak cutting tools has some affordable longer endmills. I have had good luck with them, but I have been cutting softer materials. Extra Extra Long Carbide End Mills, Solid Carbide End Mills Extra Extra Long Series
     
  11. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    MG,

    You've entirely missed the point here....

    It's not about using 3" bits. It's not about reaching all the way down to the bed. It's not about whether or not the plates have the correct holes in them. It's about maximizing throat depth while minimizing leverage on the system.

    The concept shines in a number of areas. When applied to the original ox it allows for cutting 1 1/2" stock rather than just 3/4" stock without jacking up the x axis and inducing more flex into the system. It allows more room for using vises and heavier jigs to hold stock. In that the bit fully retracts above the lower Z-axis plate, materials can be set just a hair below the axis plate reducing the lateral leverage causing flexure in the system. This can make a substantial difference when cutting metals because you're using the machine at its stiffest. As far as plates not having the necessary holes, I'm not a purist. I consider any system from OpenBuilds to be nothing more than a starting point and will alter it in any way necessary to turn it into I feel it needs to be. While I understand your issues with this as a commercial system builder, you're in the minority here. Most are building one-offs and take no issue doing what's necessary to achieve the best possible system for their needs.

    And no, I would never use a 3" bit. They're not stiff enough for cutting anything more substantial than foam, are hard on the spindle bearings, and they exaggerate runout. But this method will allow you to cut a 2 1/2" deep bowl in 3" thick wood with only a 1 1/2" bit extension. Can't do that with a plunging-Z without jacking the X-axis way up to accommodate shifting the spindle farther down.
     
  12. Exodon

    Exodon Well-Known
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    Nice comments guys ;)

    I think in general one of the points that is clear is what MG said:
    This will for sure increase the strength of the movements.

    But we have to be honest, based on a lot of builds the Z-Axis design stay always the same and if you analyse the Z-Axis movement are dependent on 6 wheels ( 3 each side ).
    If you see based on this photo:

    weakpoint.png

    I don´t know exactly, but at least 1kg is dependente on 6 wheels, why not put in the back of the C-Beam a 2080 profile and increase the wheels to 12 wheels( 6 each side). I hope you guys get the idea. Today I will try to make a sketchup.
     
  13. Metalguru

    Metalguru Master
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    I agree fully. The weak point in the OB Z axis is the 6 wheel setup. Just doesn't have the support needed for good stiffness. In my Ox HD design, I increased it to 8 wheels, and it helped a bit. I've been trying to figure out a way to use double rows of wheels, but it's a difficult problem. Just adding another row of wheels doesn't really help if the axles are unsupported on the outside. I think a design based on MG series linear slides rather than wheels would be better.

    I'm working on a design for a machine using all MG type linear rails. It should be stiff as heck, especially since I an using 2 c-beams as the X axis. This is another weak point with machines like the Workbee, the longer the X axis c-beam, the more it flexes both laterally and torsionally. Ultimately, the amount of flex is determined by the stiffness of the X beam, and no amount of beefing up the Z axis will cure this.

    MG
     
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  14. Exodon

    Exodon Well-Known
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    Thanks MG...Basically you read my mind. I didn´t bought the WorkBee or other Openbuild kit yet because of the wheel system and the Z-Axis design.
    I never built any machine, but in the last 6 months I have been studying and checking a lot of designs and know I think I have enough information to build something more strong based on C-beams. Right now I´m fine tuning the design and soon is finish I will share to get some feedback.

    Is funny when you said "2 c-beams as the X axis". I´m doing exactly but for Y-axis.

    I believe the Linear rails might be the natural evolution of the "openbuild machines"
     
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  15. sharmstr

    sharmstr Veteran
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    @Metalguru First, I really appreciate how much time and info you put into this forum. It has helped me a lot. Given the flex in a machine like the Workbee, especially the 1510, do you think its better to ramp into a cut or plunge. My first few test cuts used plunging, but I had some issues. I figured out that one of my y belts had become lose. After fixing that, I switched to ramping. The piece came out great except for the tearout at the top of the cut. I didnt have this with plunging. I can probably attribute this to the compression cutter I'm using in that at the top of the ramp, its using the very bottom of the cutter. In any case, now that I have been able to make a decent part, I'll try plunging again, but wanted to get your take on it. My setup is a Dewalt 611, 2 on the dial, .25" compression cutter in MDF (cant remember my feed rate off hand). 2 degree ramp to a 2.5 mm doc per pass.
     
  16. Metalguru

    Metalguru Master
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    Thanks for the kind words, Sharmstr.

    Unfortunately, I haven't had much experience with compression bits. It seems to me that you are going to get tearout if you don't take the bit down so that the transition point of the bit where the up and down cuts meet is below the top of the work. This means that you would have to plunge quite deep, and use a very slow feed rate. Doesn't sound optimal. Also, compression cutters don't clear out the sawdust very well, they tend to make it accumulate in the cut. Again, not optimal.

    Seems to me it would be better to use just a plain upcut or even a straight flute bit to do a roughing cut, then use the compression to shave off the last bit of material in a finishing pass. This should give you a much cleaner edge. Also, this would help with the sawdust accumulation in the cut. Considering the cost of a compression bit compared to other bits, it would seem prudent to minimize the use of the compression bit, as MDF is very abrasive.

    As far as ramping, this is usually the recommended way to use a compression or downcut spiral bit. Plunging tends to build up material in the bottom of the cut, causing a lot of friction on the face of the bit which can overheat and damage it. This can also cause a fire, particularly with MDF. This is particularly bad if you have dust collection, which you should with MDF at any time. Most sites that I looked at do not recommend using a downcut on MDF. This problem does not occur with upcut bits.

    You may not be able to avoid a bit of tearout while the bit goes into the work until it's past the transition point. If possible, ramp the bit into the work outside the actual cutting area, then move to the actual cut line. This is called "lead in".

    Perhaps also using a compressed air nozzle to clear out the kerf might help as well. Another trick I've used is to put masking or packing tape over the cut before cutting. This helps to minimize tearout.

    That's all I got. Anyone else used compression bits a lot that could lend some assistance?

    MG
     
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  17. sharmstr

    sharmstr Veteran
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    Got it. My first attempts used lead ins and outs, but I was plunging. I'm not particularly sold on the compression bits, its just what I have on hand. Thank you!
     
  18. sharmstr

    sharmstr Veteran
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    @Metalguru Thank you again for the assist. Ditched the compression cutter for an Amana downcut and the finish is great. No chatter and can cut faster.
     
  19. Metalguru

    Metalguru Master
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