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Thread: Designing a new router called Brevis-HD

  1. #101
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    Default Re: Designing a new router called Brevis-HD

    Hi Peter, are you attaching the gantry beam to the two Y-trucks with the inside screws on the trucks?

    Designing a new router called Brevis-HD-gantry-1-jpg

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    Default Re: Designing a new router called Brevis-HD

    Hi David - There is an extra bolt maybe two via the Tetrium-S "spacer or bearing beam" (see attached image) Scoot my first machine did the same and has worked well. Originally I was going to use a bracket on the outside to tie in the gantry to the other bearing holes but space (flaring allowance etc ) is too small. Its still on the ToDo list to see if this can be improved... I troll through thru the structure and address things on the list or things I don't like... still tidying the fallout from the motor mount change...

    Because the gantry is driven both sides and attached both sides seems there's not much torque on here so the friction of the 2 screws per car seems to be Ok... Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-gantry-connection-jpg   Designing a new router called Brevis-HD-scoot-2-jpg  


  3. #103
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    Default Re: Designing a new router called Brevis-HD

    Hi David - I was working on the gland bracket when you chirped in. So I've added an extra hole in the spacer block. So now there's 4 primary bolts to the cars and 4 secondary via the spacer. They will deal with the torque if any. I'm happier with this area now, so back to the saddle. I'm building a hiking trailer at the moment so I'm out to the shed to do that now. Plus I'm getting in some scrap gal 3mm to have a play with from the metal guy. I intend to solder the saddle together. Cheers Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-doubler-1-jpg   Designing a new router called Brevis-HD-doubler-2-jpg   Designing a new router called Brevis-HD-saddle-1-jpg  


  4. #104
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    Default Re: Designing a new router called Brevis-HD

    Hi Peter, I wasn't thinking about any horizontal plane movement (out of square) as that should be handled by the two motors for Y and A. I was more concerned about the twisting loads on the gantry beam resulting from cutting as your original four bolts were located more towards the inside of the U-channel of the beam. In that regards, the additional bolts as shown would not help much as they are even closer to the centerline of the channel.

    I liked your sketch with the brackets on your previous response better as I think that they would be better suited to transfer any twisting loads from the beam channel onto the trucks.

    Designing a new router called Brevis-HD-gantry-connection-jpg

    BryggaCNC.com


  5. #105
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    Default Re: Designing a new router called Brevis-HD

    Hi David - Whats in my head is to use these; brackets for construction extrusion. I've had a couple of goes at it and failed. But now the drive nut connection and bottom gantry thickness is final I can re visit these. Plus the twisting load you are describing needs some internal shear plates at the ends to stop the section lozenging, again in the ToDo. They have appeared and disappeared for various reasons.. So many rabbit holes. Peter

    https://www.makerstore.com.au/produc...orner-bracket/

    The doublers and some brackets will be epoxied into place. For a couple of decades I stayed away from friction connections because one of my lecturers said "never trust friction" and to a point yes. My early years were with welded structures and I looked at bolts as poor cousins. But in the last decade I have had to deal with small and large bolted assemblies and have come to appreciate and understand friction much better. Especially now software makes it relatively easy to analyse a bolted connection...But epoxy is even better!! Peter



  6. #106
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    Default Re: Designing a new router called Brevis-HD

    Hi David - Usually I make "square sections" trapezoidal and this gantry started out that way. Square shapes vibrate easily and lozenge easily. I straightened it up some time ago so I could use commercial brackets vs having them made. To be effective the bracket needs webs on its sides, that why I liked the cast brackets vs a made bent one with no webs. Peter



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    Default Re: Designing a new router called Brevis-HD

    Hi David et al - Since this connection has been questioned and I question it too, I set it up as a contact model. Just the connection not the whole model. To explain. The faying surfaces have been given a friction co-efficient of 0.25 (estimated low value) structural steel use 0.3 to 0.35 regularly. The connection is preloaded via the bolts tension which I applied. The solver calculates if the joint will open or close, and what bearing pressure is under the bolts and if the joint slips sideways etc. I placed a 1000N load at the clamp pushing backwards as per my usual case:

    Images

    1) The detail in question - connection 2 the little marks on the bolt heads indicate they are preloaded
    2) YaG600 global is the global push deflection of 0.33mm at 1000N which is 3N/um static stiffness which I'm happy with for now
    3) opening 1 displays the joint opens 0.091mm and where. This is under the doubler. The gantry to spacer gap is similar
    4) traction or bearing stress shows that under the rear bolt head the pressure is 32MPa which is acceptable
    5) connection 1 shows how the area deflects (exaggerated)

    I only put in the 4 screws into the bearings,. The other 4 screws will control this a bit better. Where the extra bolts are the p[late lifts so the extra bolts will stop this from happening. Overall looks good considering tool loads will be 1/10th of this in general. Plus I will epoxy the doubler to the gantry so it will distribute load even better then friction.... I can model bonded joints as well more set up required and it's too early to muck about with those things yet. The aim of the doubler is to get stiffness out to the edges which it does (seems so far) Peter

    I think the extra brackets at the moment are a "nice to have" vs a must have so onward to the saddle details.

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-yag-global-push-jpg   Designing a new router called Brevis-HD-connection-1-jpg   Designing a new router called Brevis-HD-opening-1-jpg   Designing a new router called Brevis-HD-traction-bearing-stress-1-jpg  

    Designing a new router called Brevis-HD-connection-2-jpg  


  8. #108
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    Default Re: Designing a new router called Brevis-HD

    Hi All - Another way to look at this is; Because one end is bonded and the other end is bolted we can look at the difference in deflection. The bonded end deflects 0.028mm and the bolted end deflects 0.038mm so only 0.01mm delta. So I'm happy to not consider the outside brackets at the moment. Bigger fish to catch. I've looked at the saddle and its good to go. So now to review the Z axis. Being 6mm SS I'd like to investigate if 2x3mm gal can do better....Have a web going back and one going fwd to form an I beam vs a channel...Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-bolted-end-jpg   Designing a new router called Brevis-HD-bonded-side-jpg  


  9. #109
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    Default Re: Designing a new router called Brevis-HD

    Hi All and Sundry Lurkers - Last study for the evening. Now I'm on a 3mm gal trip and I have a quote for this tool plate in SS and plain steel I looked at doing this 2 ways. 1) a 6mm SS plate bent one way 2) Use 2x3mm gal sheets epoxied back to back to form an I beam. From the quotes the 2x3mm parts will be cheaper then the 1x6mm SS part. So FE outcome.

    1) The 6mm SS version deflects 0.98mm under 1000N load. This is supported and loaded different to the router so don't compare to the router models.
    2) The constructed I beam deflects 0.75m so is 24% stiffer. So which way to go?

    The I beam is a large end to get into something if you need to do deep bowls, but then the channel will be just the same on one side. That's why I have ER extensions.... I'll sleep on it. But cost and stiffness win, unless its ugly. Ugly design always losses, is it ugly?...

    Regards Peter

    Looking at a very exaggerated deflection plot we can see that the Z axis and saddle don't deform much. Its the gantry thats really deflecting, so it's the gantry that is the limiting factor (3mm sheet) or I address the gantry (make it thicker). Seems it's time to think about the big picture and what this machine has to do.

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-z-axis-jpg   Designing a new router called Brevis-HD-beam-jpg   Designing a new router called Brevis-HD-3mm-vs-6mm-jpg  
    Last edited by peteeng; 03-29-2020 at 06:23 AM.


  10. #110
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    Default Re: Designing a new router called Brevis-HD

    Hi All - Would everyone pester the admin here to allow MP4 videos to be uploaded. Would make showing various things so much easier. The windows format allowed is too big and hard to produce. Peter



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    Default Re: Designing a new router called Brevis-HD

    Hi All - This morning did a sensitivity analysis on the gantry. The baseline version is 3mm bottom and top with a 1000N load. The baseline version deflects 0.33mm. With a 6mm top/3mm bottom it deflects 0.50mm and with a 6mm bottom and 3mm top it deflects 0.30mm. The 3mm thick bottom is the culprit, it lozenges. This is consistent with other designs I have worked on. So the economical question is: Is the 0.03mm gain worth the 6mm SS bottom for this machine? Will think that through and get quotes either way. This lozenging has been a interesting study in various machines, You can either have internal webs which is not ideal because if the bearings are between webs then the deflection is more then at a web or you can thicken the corners until this stops. Thickening the corners means thickening everywhere usually. This is where the composite will be good as I can thicken the corners easily.

    For now I think the 3mm is the go and I have to work through the gantry and check for flare and fits. very close to final checks now... Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-6mm-thick-bottom-jpg  


  12. #112
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    Default Re: Designing a new router called Brevis-HD

    Hi All in lockdowns - To recap the bearing stiffness stuff. Bearing manufacturers publish their bearing stiffness. For instance see attached for Hiwin 20mm square cars. The vertical stiffness of high preload cars is about 400N/um. Cars are about the same stiffness in all directions. The main difference is that in the vertical up dirn you are pulling on bolts so its slightly less stiff then pushing down, which is into the foundation, If steel then very stiff, if into a construction extrusion then the foundation is not very stiff. So how do we model this? I build a model of the car and rail and then adjust the car material stiffness until I get the desired deflection. So in the images I have used 4000N with a target deflection of 10um. 10um is picked up from the Hiwin charts. This is not exact for various reasons but is better then not accounting for it. Works out that the 20mm car needs to have a modulus of 15GPa. This is quite soft as aluminium is 69GPa but it's the geometric and material average required to get the design stiffness (or stuffness as the NZers would say) So I have created a material called Bearing Car and shall use that going fwd. Cheers Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-jpg   Designing a new router called Brevis-HD-trans-jpg  
    Attached Files Attached Files


  13. #113
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    Default Re: Designing a new router called Brevis-HD

    Hi All - So this is where I'm at:

    1) Machine is made from 3mm german galvanised mild steel and 6mm S304 mainly. The saddle has some 10mm in it
    2) I had to make the gantry 60mm wider so it covered a 1210mm wide sheet
    3) Happy with Z axis and saddle very stiff
    4) the std gantry is 3mm thick and I'll make a 6mm SS thick heavy version as an option
    5) The saddle will be soldered together
    6) Everything else is pretty mainstream. I have motor mounts on way from taiwan (SYK) and once I get the detail dwgs done can get quotes for all the motion parts
    7) The column spacer will be a Tetrium part which is a metal fibre epoxy matrix material that I make.

    Now its detailing out the machine base and start making drawings... Regards Peter

    Attached Thumbnails Attached Thumbnails Designing a new router called Brevis-HD-yag600-1-jpg   Designing a new router called Brevis-HD-yag600-2-jpg   Designing a new router called Brevis-HD-yag600-3-jpg   Designing a new router called Brevis-HD-tetrium-jpg  



  14. #114
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    Default Re: Designing a new router called Brevis-HD

    Great stuff Peter. Following your thread with interest.

    Do you have similar data for the Hiwin HG series regarding car-rail stiffness?



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    Default Re: Designing a new router called Brevis-HD

    Hi Buoyen - No but put in a request to your local Hiwin (or other supplier) supplier and they will get it for you. Or put it into the Hiwin site contact....Regards Peter



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    Default Re: Designing a new router called Brevis-HD

    Hi all lockdowns and other sundry viewers - I'm getting into drawings now which is pretty boring. Have to crank the handle as fast as possible to get through this stage. Once done final quotes and organisation can be done. I've decided once this is done to keep going and design a full composite version of the YaG. Since all the std parts are organised and the machine base is done makes sense to develop the composite version on this platform. Now by composite I mean it will be fiberglass and epoxy. I have many years experience in building laminates and testing them so know its mechanical properties very well. I've had to do testing for marine vessels in survey, industrial structures like cranes and elevating work platforms used in high voltage environments and civil structures like pedestrian bridges and walkways. So it will be combination of infused fibreglass and tetrium.... Will be able to optimise the structure so much better in composite,,,,Will be fun. Peter



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