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How to make the HD4 more rigid

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  • How to make the HD4 more rigid

    I have had the HD4 for over a year now and have always dealt with the gantry flexing more than my liking. I have to baby every roughing cut or hold pressure on the router to keep things from bouncing around. I have already strengthened the lower support connecting the arms to the lower rails with .25 steel plate and that helped greatly with the side to side flex. However now it seems the main issue is with the flex up and down at the cutter. I feel that I shouldn't be able to push up on the bit with my finger and make the router move up and down nearly as much as it does. Hard to make accurate cuts with that much movement. Not such a deal with single tool V carve text and such, but when tiling using multiple tools this becomes an issue. I know I'm not the only one with this problem as I have seen it mentioned in other forums, Is this caused from the use of plastic instead of aluminum for the construction? I am a machinist so I have access to cnc metal working machines, but don't really want to totally rebuild the whole machine if I don't need to. What have others done to make this machine more rigid? What are the main components that need to be reworked? Could some of the flex be resolved by moving the Y rails farther apart or am I barking up the wrong tree there?

  • #2
    Hi Sky Jumper,

    I was looking at mine today, I bought mine used and have found a few things that could benefit from re-design.

    1) Dust boot with stiff brushes cause gantry shifting. I know they have a new set of brushes out, but I have not tried them yet.

    2) I have found play in the Z axis bearing holder. I had to dis-assemble mine to fix another issues and I check this, but no issue, I was puzzled. After re-assembly I check the gantry play and it was there. Holding a finger at the top of the z axis bearing, you can feel the play there. I'm thinking it's a weight issues and the material they used to make the gantry. I have notice that you can push a finger nail into the material and it will leave a mark. This tell me it's a soft material.

    I'm toying around with the idea of making a new unit out of metal or a harder plastic material.


    • #3
      I have the same issue with the HD4 Extended with Water Cooled Spindle that I purchased (used but very low hours) for out HS Robotics team. We bought it with only a little research and more of an immediate need. A little different, though, in that we are using it to cut poly-carbonate and, hopefully, aluminum (have cut a little already).

      What we have found is that we get a lot of chatter when traveling in the Y direction where it "drags" the tool putting the forces against the tool and, thus, flexing the round linear rods that support the cross feed (X axis). I had to put slight pressure on the router to keep the chatter from occurring also. After seeing this I think Next Wave could have done a lot better job and eliminated this as an issue if they were to have used a supported round shaft (like the one on the bottom of the machine) to stiffen the carriage and reduce the deflection.

      So, we made the decision to redesign the top half of the machine since we already have invested in it. We will be replacing all of the travel components with heavier aluminum, riser bars for supporting linear rails (and creating a rigid cross support), and replacing all of the round rods on the top (X-Axis and Z-Axis) with linear rails and bearings (thus making it like a real machine).

      I am not sure if we will replace the acme screws yet, but we are talking about changing these out to ball screws or, at least, a zero-backlash acme nut.

      We are hoping that this takes care of the majority of the issues and lets us cut the material we are needing. At this time we are not looking at modifying the bottom rails and bearings (Y-Axis) but will evaluate that as needed (I would love to change this to 2 ball screws, one on each side and timed, to keep the carriage moving truer).

      We are in the process of designing the retrofit and hope to have it installed in July.


      • #4
        You'll find more z flex when the router is in the middle of the bed then on the edges. Those round bars just aren't the best to holding strong.


        • #5
          To Potinsky: Have you completed the redesign of the HD-4? I have an HD-4 and I am not anywhere near satisfied with it's rigidity and performance. Just by holding my spindle motor by the collet, I can move the bit 20 to 50 thou in any direction. Sure would be interested in how you did yours if you are interested in sharing any details, especially sources of the linear rails and bearings and the mountings -- maybe some pictures??


          • #6
            You can buy this from nextwave.


            • #7
              tonydude919: I saw that and I guess I will have to try it... I can't even cut maple without the bit chattering, and every once in a while, eating what I'm cutting. The item description says: "...add increased rigidity to the Y axis by adding 4 tabs to the cradle assembly..." I only see two tabs???? Not sure where they come up with the other two?? Anyway, I plan to order it and try it, looks easy enough to put in...


              • #8
                rayray: I did get a design done but not built yet. Saw the retrofit so I am thinking of trying that or finding more information on the performance. The design I did is more rigid than the retrofit so not 100% sure on my direction yet but need to decide quickly. If you got the retrofit I would be curious on how well it actually works.


                • #9
                  So, I did purchase and install the HD5 Retrofit Kit for the HD4 system back in December. Since then we used it to cut a lot of polycarbonate (up to 3/8" think) and ABS materials (up to 1/4" thick). I think we may have run some PE material (1/2") also but I can't recall. The upgrade kit is better... it does a lot better job at with the deflection and chattering. In many cases we were able to increase our cutting speeds 4x what we had to run prior. I think the design could have been a little more robust, especially in the Z Axis. We did still see some chatter on the PC materials but manageable. I did not get a chance to cut any aluminum... hopefully this summer I will play with that and can give some feedback.

                  If you are running wood materials only this would definitely be an upgrade worth considering.