# New Unistrut build - critical dimensions **URL:** \ **Category:** Hardware\ **Created:** [March 3, 2018, 2:49am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579 "2018-03-03T02:49:39Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 2:49am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/1 "2018-03-03T02:49:39Z")
My kit is in this batch. There was a sale on superstrut so I decided to buy a bunch to build a frame. I have a few things I want to include to allow to help with testing / development of the Maslow. Those include. - adjustable angle - adjustable motor width (including wider than 10’) - skirt around work area for full 4x8 cutting area. I was wondering what the critical/starting dimensions should be. Most importantly 1.) the distance between the two motor sprockets 2,) the height above the top of the cutting area the sprockets should be 3.) the angle of the work surface from vertical. Thanks, Chris ---
**Author:** ![Bee](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/bee/32/2160_2.png) [@Bee](https://forums.maslowcnc.com/u/Bee)\ **Post date:** [March 3, 2018, 4:49am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/2 "2018-03-03T04:49:22Z")
I can answer 2 out of those 3. The Distance between is subjective, I think most desings are 10ft at this point. The optimum angle is 10 - 17 degrees. The average motor hight is approximately 18 inches from the top of your work piece. I’m just repeating what is out in the forum. Thank you ---
**Author:** ![dlang](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/dlang/32/859_2.png) [@dlang](https://forums.maslowcnc.com/u/dlang)\ **Post date:** [March 3, 2018, 5:40am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/3 "2018-03-03T05:40:24Z")
> I was wondering what the critical/starting dimensions should be. Most importantly > > 1.) the distance between the two motor sprockets > 2,) the height above the top of the cutting area the sprockets should be the stock machine has the chains go from about 10 degrees to 80 degrees, and we run into problems at both extremes. This is with the motors about 12" to the side of the work area, and about 18" above the top of the work area. The biggest problem is the side distance, with the motors 12" to the side of the 4x8, we really struggle in the bottom corners where the chain angles are the worst. We believe that moving the motors out a bit (to about 12’ rather than old stock 9.7’) would make a significant difference. On the top, we have had one person with an extra heavy sled run into problems with the motors not being able to pull hard enough to move the sled at the requested speed. There does not seem to be a big driver to go higher, and going lower would make it easier to run into this problems. > 3.) the angle of the work surface from vertical. The last testing that we did on the angle was a long time ago, before triangular kinematics were introduced (let along chain sag compensation), and that showed that angles below about 10 degrees or above 15 degrees didn’t work well. With triangular kinematics, the sled rotating due to the motor torque is not going to cause an error the same way it would before (if it moves too much to where the linkages/ring can no longer rotate it can cause an error, but still less than what was caused by any rotation under quad kinematics) I suspect that with triangular kinematics and chain sag compensation, you can go steeper (closer to vertical) without running into the problems that we had before, which would improve the accuracy as more of the weight would be etting applied to the chains rather than causing friction to the work surface. But we do not have anything close to current testing of this (I asked for someone to do a series of tests on this last week, but so far nobody has had time to do so) ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 8:02am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/4 "2018-03-03T08:02:29Z")
Thank you for the feedback. I’ll have to draw out some dimensions to work out angles, but if I make a top rail of 12’ to allow more space with the motors, should I be raising the height above the work piece at the same time a bit? ---
**Author:** ![dlang](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/dlang/32/859_2.png) [@dlang](https://forums.maslowcnc.com/u/dlang)\ **Post date:** [March 3, 2018, 8:19am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/5 "2018-03-03T08:19:46Z")
I would start off not raising it, raising it will undo some of the benefit from widening it. just watch for problems along the top (especially top center) and if you see them, consider raising it (and tell us the results) k ---
**Author:** ![LakeWorthB](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/lakeworthb/32/4071_2.png) [@LakeWorthB](https://forums.maslowcnc.com/u/LakeWorthB)\ **Post date:** [March 3, 2018, 11:34am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/6 "2018-03-03T11:34:30Z")
Does the stock chain length support 12’ motor spacing? ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 3:43pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/7 "2018-03-03T15:43:04Z")
Thanks @dlang Adding height to the top of a unistrut frame would maybe not be ideal. I think if I determine a maximum height I might want to use I can build the frame to that, and then adjustment would just mean moving the bottom rail up and down. (Or clamping a bottom skirt higher or lower to effectively change the height) I believe I will have to order some more chain and master links to extend the chains for these dimensions. ---
**Author:** ![blurfl](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/blurfl/32/9_2.png) [@blurfl](https://forums.maslowcnc.com/u/blurfl)\ **Post date:** [March 3, 2018, 4:08pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/8 "2018-03-03T16:08:50Z")
The stock chains are only long enough for a 10’ top beam. Adding a couple feet on to the ends of the chains is easy to do, though. ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 6:26pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/9 "2018-03-03T18:26:05Z")
I have ordered a a 50’ roll of #25 chain to use for the larger frame. I was thinking of trying a section of chain in a loop on the bottom with a spring retracting cable or bungee to attach to the bottom of the sled that could be controlled by a motor to move the point of downwards/sideways pull to increase accuracy towards the sides. ---
**Author:** ![dlang](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/dlang/32/859_2.png) [@dlang](https://forums.maslowcnc.com/u/dlang)\ **Post date:** [March 3, 2018, 6:29pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/10 "2018-03-03T18:29:13Z")
no, you need about a foot more chain to do 12’ motor spacing ---
**Author:** ![blurfl](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/blurfl/32/9_2.png) [@blurfl](https://forums.maslowcnc.com/u/blurfl)\ **Post date:** [March 3, 2018, 6:29pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/11 "2018-03-03T18:29:37Z")
That’s an interesting approach, keep us posted! ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 6:31pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/12 "2018-03-03T18:31:28Z")
I don’t think th current board has support for a 4th motor, but a manual manipulation of the bottom chain could be done to test if it would be worth it. It should be pretty easy to implement if a controller was available on the board. ---
**Author:** ![dlang](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/dlang/32/859_2.png) [@dlang](https://forums.maslowcnc.com/u/dlang)\ **Post date:** [March 3, 2018, 6:37pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/13 "2018-03-03T18:37:55Z")
give it a try, but you will have to disable the chain sag compensation code as it won’t followthe same model. David Lang ---
**Author:** ![blurfl](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/blurfl/32/9_2.png) [@blurfl](https://forums.maslowcnc.com/u/blurfl)\ **Post date:** [March 3, 2018, 6:42pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/14 "2018-03-03T18:42:53Z")
I haven’t looked deeply into the chain sag compensation, but I think it is calculated, based on measurements taken during calibration. It’s possible that the calculation would accommodate this modification if it was an active part of the calibration. It would be interesting to see. ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 3, 2018, 6:54pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/15 "2018-03-03T18:54:34Z")
That would definitely be a requirement for it to add any value. It would make sense that is how it’s calibrated as I think there would be numerous factors that could affect chain sag which would vary build from build, so a fixed chain sag compensation would not be ideal. Haven’t looked into it at all either though. Just a thought that popped into my head an I’d like to contribute. ---
**Author:** ![commonthings](https://avatars.discourse-cdn.com/v4/letter/c/f475e1/32.png) [@commonthings](https://forums.maslowcnc.com/u/commonthings)\ **Post date:** [March 3, 2018, 7:21pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/16 "2018-03-03T19:21:39Z")
You might have a look at the unistrut based frame I posted on the Advanced Frame Design thread last week: > [@Advanced Frame Design](https://forums.maslowcnc.com/t/advanced-frame-design/2245/4): > > Here is the frame I’ve designed for the Maslow. I’ll need to fine tune it when my kit arrives, but this is what I have at this point. I know, I know, the first thing that comes to mind is “this is totally overbuilt”. However motor to substrate rigidity is essential to the Maslow design. Even a millimeter of flex in the frame contributes to less accuracy in the cut. There are several issues I’ve tried to address with the construction: Rigid construction to reduce flex in motor supports under lo… I’ve used a 12’ top beam 2’ above the top edge of the cut area to reduce problems with extreme chain angle. The chain distance and frame angle are adjustable for work with various materials. I paid particular attention to making the frame as rigid as possible. My kit has not arrived yet for fine tuning details on the frame. Dlang had a great idea for adjusting the top beam for proper chain distance with a block of the wasteboard or cut material that I will be implementing. ---
**Author:** ![dlang](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/dlang/32/859_2.png) [@dlang](https://forums.maslowcnc.com/u/dlang)\ **Post date:** [March 4, 2018, 12:48am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/17 "2018-03-04T00:48:44Z")
we are narroing down on the critical factors for the height above the workpiece. Bar finished building the new frame design today, and he made one change to the design, and that made it so that the motors are clearly too low (at 15.5" from the top of the workpiece to the top of the motors) I’ve asked him to try at 17" to see what happens, and then again at 19" if that doesn’t work. ---
**Author:** ![eppic](https://avatars.discourse-cdn.com/v4/letter/e/e9bcb4/32.png) [@eppic](https://forums.maslowcnc.com/u/eppic)\ **Post date:** [March 4, 2018, 5:38am UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/18 "2018-03-04T05:38:29Z")
Thank you for the feedback. I’ve seen your thread and the two other bigger unistrut threads. I think for the time being I’ll be taking ideas from across them all. I love your build, but I think I want to keep things more simple and more easily changed as this seems to be a pretty dynamic project. I will probably just have skirts I’ll make in appropriate thickness I clamp on to the steel frame as needed instead of building all that structure initially, until I get some actual Maslow time under my belt when my kit arrives. Inspiring build though! I like your hinges for angle adjustment. One of the reasons I like the unistrut idea is that it can be tweaked so readily without having to build a new frame. It will be interesting to see what the Maslow design can do in a year from now. ---
**Author:** ![commonthings](https://avatars.discourse-cdn.com/v4/letter/c/f475e1/32.png) [@commonthings](https://forums.maslowcnc.com/u/commonthings)\ **Post date:** [March 4, 2018, 3:11pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/19 "2018-03-04T15:11:55Z")
I agree - making the structure so that it can be easily changed. Everything on my current frame is either bolted or screwed together: flexibility in the design (not in the frame!). I am still not satisfied with my skirt attachment. It can be changed by substitution or shimming but that is not as easy as I would like. If you find a good way to clamp the skirt please post it as well as your design as you build it. Thanks, Paul ---
**Author:** ![commonthings](https://avatars.discourse-cdn.com/v4/letter/c/f475e1/32.png) [@commonthings](https://forums.maslowcnc.com/u/commonthings)\ **Post date:** [March 4, 2018, 3:26pm UTC](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579/20 "2018-03-04T15:26:08Z")
I’m interested to see where the motor height testing goes. What are the problems presented by the 15.5" height? [Next page](https://forums.maslowcnc.com/t/new-unistrut-build-critical-dimensions/2579.md?page=2)