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  1. #1

    Plywood disaster in progress!

    Hey boys and girls, after intensively lurking on this forum for a bit i hereby create my first post and start of my project log! A CNC router made from plywood!

    My own design, based around a makita rtc0700c handheld router, Arduino Uno and SBR20 rails.









    As you can see the design is still in the early stages. The goal of this project is to get a start in the CNC world for a low price, and expand from there.

    The frame parts will be made of 18mm Plywood. The Uprights for the Y-axis are two glued sheets of plywood, aswell as the sides for the bed frame. The gantry is comprised of a total of 5 sheets for maximum stiffness.

    Motion is transmitted by two T10x15 belts on the Y-axis, and bearing spindles on the X and Z axis.

    I hope to update this log regularly with exciting progress, in the meantime i'm looking forward to your thoughts on the design!

  2. #2
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    Re: Plywood disaster in progress!

    Hi Sjek - Looks good. make the gantry more of a box. Your columns are very stiff which is very good. You don't need so many cross boxes in the base. I've used the makita and its great but its very noisy. I suggest you look at 600W 48V DC spindle. Been a great upgrade to my machine and the cost is about the same (maybe less). I'd pick an ER11 collet as they are smaller (vs a ER17). I do deep things this may not be a concern for you. T10x15 belts require a much bigger idler then you have drawn. Get hold of a belt manual for this info. You will fatigue the belt quickly with such a small pulley and idler. It will be a very good machine, plywood is a great material. Use a good epoxy or urethane glue. Peter

  3. #3

    Re: Plywood disaster in progress!

    Peteeng, thanks for the tip about the belt, hadn't thought of that and after checking the belt it would seem my idea wouldn't work, so i changed it to a larger diameter pulley (60mm).

    I made some progress in drawing and it's going quite swiftly i must say! The next thing is the Y-belt tensioner, now it's just pulled tight and clamped down with bolts, but i'm wondering if perhaps some sort of mechanism where a bolt tensions the belt is necessary, any thoughts?

    I also wanted to use threaded inserts in some places, but i'm starting to doubt if these will be strong enough, i want to use them in both the front and the sides of the plywood, but i'm afraid they might tear out or turn with the bolts. Any experiences with using threaded inserts in plywood? Perhaps using epoxy to glue them in place?


  4. #4
    Community Moderator ger21's Avatar
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    Re: Plywood disaster in progress!

    Some gear reduction on the belt drives would be much better if possible.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
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    Re: Plywood disaster in progress!

    I would say it needs about 1:5 gear reduction even if you use the smallest pulley available for the T10 belt (which is 12 teeth). As of now, you have 120mm of travel per turn, or 0.6mm per full step. Way too much.

  6. #6
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    Re: Plywood disaster in progress!

    Hi Sjef - Threaded inserts are very good. I use them alot in timber. They are really only needed in places where you are going to pull the screw in and out a lot. If the screw is intended to be permanent use a Kreg screw or a std threaded screw but epoxy it in. I drill a pilot and use a tapered thread tap. In this way the screw gets tighter as it goes in. Once I have the parts or machine set I go around removing the screw and use PVA glue or epoxy (I use 5 min epoxy for screw setting) to set the screws. If you want the screw to come out one day and you are using epoxy you need to wax the screw. If you don't then warm the screw with a soldering iron and it will release easily. PVA seems to lock the bolt well and can be screwed out easily so use that.

    I haven't set inserts in the past but I have spoken to people who have epoxied them in and have had to chase the thread afterwards. I'd use PVA to set the insert if you where concerned.

    Belt tensioning is a must. The tighter they are the better they work. To a point. I personally don't like omega drives, prefer a full loop. This is because of the backbend in the system requiring a large idler to reduce fatigue. If you use a single loop then you can use a small driving pulley and same size return pulley. The issue with a full loop is that it is half the stiffness of the omega drive style. But then you can use a wider belt to compensate. I also try to make the motors fixed vs riding with the gantry (to lesser the gantry weight and make wiring simpler) and the single loop achieves this.

    https://www.ebay.com.au/itm/Threaded...-/192886654066

    I use this style of insert... Peter

    You need to do some maths with the pulley size. A large pulley will give you incredible speed but not much force. Depends on what you want the machine to do.

  7. #7
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    Re: Plywood disaster in progress!

    Hi Sjef - When the z axis is at bottom is the critical point for stiffness. You need to have the z axis thicker at this point. A-A in image. You have compromised the z axis by considering the Makita lead, move the lead or use a 48V 600W DC brushless spindle. The 48V type is smaller and better in my opinion.

    https://www.ebay.com.au/itm/200W-300...-/132273974879

    You will be disappointed with using small tubes for motor standoffs. Better to make a ply base. They will deflect under the required belt tension. Peter

    I've attached an image of one of my benchtop machines. Will cut plastic, timber etc no problem. Uses N23 motors. You can see the belt has a single loop. It uses T5-10mm wide belt. It was intended as a plotter, knife machine not a router. Look at T5 belt then you can use a smaller pulley. I also use 400 step/rev motors. More accurate if that's important. On bigger machines I use 16mm wide or 25mm wide belt.

  8. #8
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    Re: Plywood disaster in progress!

    I have used the pronged T-nuts for some jobs and I have used the knurled Tappex inserts,set in epoxy ,for others. https://www.tappex.co.uk/products/br...erts/multisert . In both cases the holes need to be positioned pretty accurately.

  9. #9

    Re: Plywood disaster in progress!

    Quote Originally Posted by CitizenOfDreams View Post
    I would say it needs about 1:5 gear reduction even if you use the smallest pulley available for the T10 belt (which is 12 teeth). As of now, you have 120mm of travel per turn, or 0.6mm per full step. Way too much.
    Quote Originally Posted by peteeng View Post
    Hi Sjef - When the z axis is at bottom is the critical point for stiffness. You need to have the z axis thicker at this point. A-A in image. You have compromised the z axis by considering the Makita lead, move the lead or use a 48V 600W DC brushless spindle. The 48V type is smaller and better in my opinion.

    https://www.ebay.com.au/itm/200W-300...-/132273974879

    You will be disappointed with using small tubes for motor standoffs. Better to make a ply base. They will deflect under the required belt tension. Peter

    I've attached an image of one of my benchtop machines. Will cut plastic, timber etc no problem. Uses N23 motors. You can see the belt has a single loop. It uses T5-10mm wide belt. It was intended as a plotter, knife machine not a router. Look at T5 belt then you can use a smaller pulley. I also use 400 step/rev motors. More accurate if that's important. On bigger machines I use 16mm wide or 25mm wide belt.


    Thanks for the tips!

    I was already in the progress of doing some FEM, with the following results:






    A load of 300N was applied to the router mount in Y-direction (first image) and then in X-direction (second photo). As seen in the displacement legend on the left, deformation is quite minimal. I will probably reinforce the Gantry uprights though, but i'm not seeing any problems with the strength of the router mount.

    mechanical properties of Plywood found here: Plywood

    I am aware that this simulation is unreliable at best, but i just wanted to see what would happen. Basically nothing surprising so i'm happy with that!

    I was planning on microstepping my stepper motors, my knowledge of electrical stuff is a bit limited so i don't know the drawback of microstepping, lost accuracy? less torque? I hadn't thought of the resolution in the y-direction, but seeing that it's 0.6mm per step is quite alot, so i'll be adding that reduction to the design, along with an improved motor mount.

  10. #10
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    Re: Plywood disaster in progress!

    Hi Sjek - Plywood is orthotropic and your probably using an isotropic solver. So use the lower values. Plywood is a laminate and its cross plies do not contribute to the stiffness much. So the actual plywood stiffness depends on the bending direction within the structure. What you can do is clamp a piece of plywood on a bench in a cantilever and put a weight on the end and measure its deflection. Then model the set up. Then you can tune the E to match your test.

    I see in image 1 the kink that I expected to be there, very good....

    Microstepping is used to smooth the motor action. If you use a setting of around 2000usteps to the rev that would be a good number. Here's a link to good explanations for you on drivers. Peter

    https://www.geckodrive.com/support.html

  11. #11

    Re: Plywood disaster in progress!

    Pictures update! Started breaking down large pieces of wood into smaller pieces of wood.




  12. #12
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    Re: Plywood disaster in progress!

    Hi Sjek - Yes bond paper has the same mechanical properties as MDF. So you should be able to make the machine out of the drawings. Peter

  13. #13

    Re: Plywood disaster in progress!

    Update! I'm steadily progressing toward imminent failure or success, let's see what it will be. Today i finished fabricating the parts, namely gluing up the torsion box that will act as my base. Everything has been cut to size, drilled and glued and next up is assembly.






    Extra pictures here: https://imgur.com/a/3XPaeSo

  14. #14

    Re: Plywood disaster in progress!

    First cuts! used the router to mill some holes for workplace clamping.

    https://imgur.com/njDIlam

    However now i have another problem, i'm using an Arduino Uno with GRBL (no breakout board) and have wired up some simple NC endswitches. However they regularly trigger the alarm without being mechanically triggered. Anyone have any experience in this regard?

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