The "Special Topics" blog posts focus on additional design
details, testing, & performance of my CNC Router
details, testing, & performance of my CNC Router
One of the first things I realized after the machine started cutting was the amount of mess created. Chips were not only flying around the shop but creating a major problem by littering the table X-axis rails and ball screw. In this post I’ll describe my recent addition to my router by detailing the machine enclosure. I’ll start with the list of requirement, get into the design, pics and video of build, and then offer some alternatives which I investigated along the way. "Enclosure" is a term used loosely here as you'll see it's not your typical containment box approach.
OK ... enough of that. It's just that this list proved extremely helpful for me to write down as I found myself struggling to come up with a sufficient design for my specific router build.
Below you'll see the complete CAD design. It's a bit unconventional for a "Machine Enclosure" as it's split into a combination of multiple approaches. The design can be broken down into three main sections: 1) The 'conveyor' protection for the table linear rails and ball screw, 2) The rear guard/shielding, and 3) The front/spindle shields.
The protection for the X-axis Table is the odd ball design here. I haven't seen this approach used yet and as I write this post, although I'm parts complete and ready to assemble, I've yet to verified it works (fingers crossed). .... well, just ran the table with conveyor attached - works much better than expected for first try. Will post a video at the end of this post - kinda cool.
You may say, "why not just mount 4 walls directly to the moving table".... First, the Y-axis gantry motion is allowed to move the spindle beyond the extent of the table which would then crash into the side walls. Ok, then make the side walls static by attaching them to the base and only attach the end walls to the moving table. I played around with this design for awhile but the drawbacks were.. a) obstructed part loading with the walls, b) used more material $ then the 'conveyor' approach, c) I didn't think I'd like the looks of the end wall on the table moving around, d) I didn't really think it wise to mount any guarding to the moving parts.
So the result is a 'conveyor' design using.... ready for it.... PVC schedule 40 pipe and a window shade. A 1-1/2" PVC section makes up the two end rollers and are mounted to the base table. They don't actual roll but I'm expecting the window shade to slide freely over the PVC. As my linear rails on the X-axis table extend about 1" over the extent of the table (I was trying to utilize every last bit of material to maximize stroke), I needed to make some cutouts for the rail and truck to move to the end position. I think the roller end position will actually 'clean up' the visual appearance of the table end. A 1" PVC section is then 'slipped' into position utilizing a slot in the PVC together with the Base 1/4" leg sections. I'm expecting this sudo-mount to be enough to retain the 1" PVC in place (again does not 'roll'). As for the conveyor material, I simply had the hardware store cut a cheap $10 window shade to width and will attach 2 pieces to each end of the moving table, wrap around the rollers, and connect them with a spring for tension. Four (or more) things can go wrong here.... 1) acceleration of the table causes the conveyor belt to buckle and flap enough to cause issues, 2) the conveyor does not ride straight and possible slips off one side, 3) the tension of the belt causes too much friction between the PVC and window shade, 4) the window shade material does not hold up to the abuse from aluminum chips and continuous rolling back and forth. Time will tell.
Below are some more details of the CAD design for the conveyor.
The rear guard is a nylon conveyor stip brush (74405T9) from McMaster Carr with a compatible holder (8813T52). I'm not concerned about visual in the rear so decided to try a brush. It's a 4" long 3/16" width with diameter 0.014" general purpose nylon bristles. It's a bit stiff and I'd probably choose the 0.010" diameter if done again. Mounting is simply to the backside of the uprights and allows 2 positions of mounting, one which allows brush to lay flush with table and another 3/4" up to accommodate a thick spoiler board. The bristles will allow about 1/2" part interference to go thru the entire length ok but any higher than this and I think it may bend the aluminum mounting strip. So it will probably allow a 2" tall part at a reduced width (~4") thru without issue as the overall force from the bristles will not come from the entire length.
The front shields are made up of Impact-Resistant 1/4" Polycarbonate sheet (8574K43 - blue in pics) & 0.04" thick Chemical-Resistant PVC Type I Film (87875K61 - yellow in pics) both from McMaster-Carr. The side shields have 4 magnets bonded in to allow mounting to the steel upright and post and allow quick removal. It also has a cutout where a single piece of film is bonded which allows the spindle to pass. The main front shield film is mounted to a 3/8" rod which is then attached to a vertical 1"-3/8" post mounted into the table with a 3/8" universal clamp to allow adjustment and quick removal. I should be able to remove all the front shields in <30 seconds for cleanup etc.
Below slideshow has some pics of the final results and in process manufacturing ....... and below that is a youtube video of the 'conveyor' in action.
I have cut multiple parts and below is some observations and things I might change if doing again.
Added a Mist Coolant system:
I absolutely needed to add a mist system - spraying wd-40 from a can was not fun. I just happened to have purchased 2 Wesco mist systems at an auction some time ago on the cheap to I went about to use as much hardware as possible from one of these units to make a custom mist to fit my router build.
The Wesco mist unit works by delivering compressed air and mist to the nozzle tip with two small separate tubes which run through the braided sleeve. The mist is then mixed with compressed air only after it exits the nozzle tip - this can be seen in photo below - focus on the brass tip end of the nozzle. A flow valve controls both compressed air and fluid independently with a manifold block which I mounted onto the z-axis. The close proximity of this flow manifold to the exit nozzle allows fast response to flow changes.
To position the nozzle I opted for a small Noga model NF1033 articulated holder which has 51mm and 56mm arms. At $75 bucks this is not a very economical solution for holding a mist nozzle but I've wanted to pick up one of these small Noga arms for the shop anyway, so "two birds". The unit comes with a 360 deg fine adjustment base attached with a dovetail to a permanent magnet which is all removed to expose a simple M6 thread to mount directly to the spindle column mounting bracket on the router. The NF1033 also comes with a 3/8" clamp holder on the business end which fits the Wesco misting nozzle perfectly.
Below are some in photos showing the original Wesco mist unit and the modifications to adapt this to the router.
The articulating arm of course moves the nozzle into position with ease and locks to exact location. The reach of the arm allows the nozzle to be located around the spindle about 270. I opted to replace the original Wesco SS coolant tank with a simply 2 liter plastic bottle which is located on the base and out of sight behind the gantry. The elevation of the coolant for this style mist unit must be below the nozzle outlet to avoid dripping when compressed air is removed and I also found that placing the tank too far below the nozzle (on the floor of the base) created too much lag time to get the mist flowing and operation was sporadic.
This post will not be about the electrical details of home and limit switches but rather on my choice of hardware and how I incorporated them into my fixed gantry design. Due to lack of experience in limit switches and the unknown accuracy they give for repeatable home position I decided to include in the X & Y axis both a set of limits and a separate (more expensive) home switch. An overview of the added hardware and location is shown in the below CAD picture. Note that v03 on the download page now includes this design.
For the Z-axis (pic below) I used a roller lever type micro switch manufactured by Renew, model #RV-125-1C25. These guys are a bit on the cheap side in quality but I wanted to limit the size mounted onto the z-axis. The toggle rail rides on the edge of the Z-axis moving plate while the limit switches are mounted onto the rear permanent plate of the z-axis. Adjustment is made with some slots in the switch brackets and the cables are routed thru the cable tray.
For the X & Y axis I was able to package a much larger limit switch and the quality of those units far exceed the Z-axis. The X-axis table (pic below) used a roller lever style limit switch from CNTD, model #CZ-7141, which is mounted directly onto the Brute machine table with an adjustable bracket and a toggle rail mounted on the underside of the aluminum fixture table. I could have located both switches inline and avoided the need for two toggle rails but this would have resulted in one of the limit switches mounted at the extreme forward location of the machine and I simply did not want to look at the switch when the table was in the extreme -X location so opted for 2 separate toggles which pushes the hardware out of view. Update: After installing the 'conveyor' to protect the ballscrew and rails from chips I got rid of the second toggle ramp on the right side and re-positioned the 2nd switch inline with the 1st on the left side.
The Y-axis gantry limit switches are button depress style switches from CNTD, model #CZ-7110. I chose this style due to the lack of space between the Z-Axis assembly and the gantry rails for a toggle style and the fact that I could 'hide' the entire switch inside the gantry rectangular beam. The button of the switch is the only part exposed into the moving path of the Y axis gantry and is actuated by a toggle ramp mounted to the back side of the rear z-axis plate. One drawback is the limited adjustability of the switch location due to the hole restriction in the tubing; therefore, adjustment is made by carefully locating the elevation of the button to the toggle ramp.
The home switches are higher quality precision contact switches purchased from Misumi (model #MSTKD-EL) at a cost of $60 each. I wasn't certain of the repeatability of the cheaper limit switches (~$7) so decided to use both on the X & Y axis and compare them. The home switches are mounted onto a simple mount made from 1" steel round machined to include both the switch and a stop screw to insure I don't damage these expensive units. Unfortunately at this time Mach4 together with my ESS (smoothstepper controller) does not fully function with both home and limit switches so I've yet to have a comparison for you - I'll update when software is fixed. At this point the limit switches seem to be very repeatable leading me to believe I don't need the separate home switch.
You'll notice that the home switch (and one limit which currently acts as home) is located directly at the fixed end of the ball screw. This is because the ball screw incurs significant thermal expansion in operation therefore for the most precise repeatability is obtained at the fixed end of the screw shaft. I was surprised to learn that ball screws typically see about 2-5 deg C thermal change in operation and this results in an expansion of 0.02-0.06 mm (0.0008-0.0023") at my maximum extended position. Also of interest is that precision machines avoid this thermal error by 'stretching' the ball screw to the estimated maximum displacement from the thermal expansion and fixing both sides of the screw shaft. This shaft now loaded in tension will simply reduce the tension load as the temperature increases and have zero overall length change due to thermal expansion. They also adjust for that stretch of the shaft by manufacturing the pitch to incorporate that stretch... Neat! They talk about how to load the shaft in tension preload and set into the fixed ends but I was discussing this with a colleague and we came up with a simpler (more diy) approach.... all you have to do is heat the shaft to a set temperature (maximum expected) and then mount 'hot' into the fixed ends and when it goes back down to 'shop' temperature it will be in tension. Just need to make sure your end supports are directly connected together with a stiff enough connection to accommodate the tension load. Oh and then have a special pitch manufactured.... ok, definitely not a diy item typically considered.
Some pictures below of the manufacturing and build (slideshow format)