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  1. #25
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    Default Re: 4'x8' vacuum table build questions

    He1957, Gerry & Aerojunkie, lease remember I'm new to cnc. I'm not sure I understand the processes, do you know of any articles or videos I can read or watch to understand better?

    On a good note I finished the plumbing today, now the only thing left is to wire the motors and attach the spoil boards.4'x8' vacuum table build questions-20190114_203831-jpg



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    Default Re: 4'x8' vacuum table build questions

    What check-valve are you using?

    David Gage
    Deep Sea Sound


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    Default Re: 4'x8' vacuum table build questions

    It isn't installed yet I have one Sean told me to get ordered on Amazon search VPV060 on Amazon on also using a pressure valve to monitor the pressure search Jegs 41008. I'm not sure how I'm going to get to the cap on the right side to drill & tap. Also now that I think of it im worried that the shavings from drilling & tapping the holes will damage the vacuum motor(s)



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    Default Re: 4'x8' vacuum table build questions

    Gary,

    WRT: Double-sided. My meaning was with your table, the X and Y T-slot intersection could be used as a 0,0 reference. Draw your part using that as G54 origin. The T-slots can have "stops" to position the workpiece (Example: a 300x200 mm blank, the center (150, 100) can be 0, 0 (T-slot intersection). Using that co-ordinate as reference, use your software to mirror your drawing and you then have a Left and Right model. Place the mirrored copy on a different layer in the software so you can select the "Left" or "Right" to generate a toolpath. The workpiece is done with the Left, flipped over then the Right toolpath.

    Another option is make a jig to hold the part as a Left and Right Model "hollow mold". Route this out (as a pocket) using the mirror technique as above a few mm shallow so the vacuum can hold it down. Since the mold does not need to move, the 0, 0 reference is the same.

    In the photo, the reference point (0,0) is the lower-left corner. The drawing is within a 300x200 mm rectangle and the center of the drawing is 150, 100. The duck image and details were mirrored using the center point to create a L and R version on different software layers and a pocket toolpath was generated to hollow out the L and R duck shapes. I then select the paths for doing the Left side engraving, flip the part and then do the Right. The mold is 12 mm plywood pocketed to 10mm. The part to machine is 18mm. The part is cut using the outside profile, the mold using the inside profile hence, the part fits in the mold like a bought one :-)

    The photo shows all my parts are wedged using the spoilboard with wooden dowel pins, blocks and wedges. However, since the mold is solid on the underside, vacuum can now hold it while the part being engraved is wedged in the mold.

    Attached Thumbnails Attached Thumbnails 4'x8' vacuum table build questions-duck_img_20190116_103330-jpg  


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    Default Re: 4'x8' vacuum table build questions

    Ok thank you, I like the idea of routing a jig

    I wasnt able to do any work on the router / vacuum table tonight but hopefully tomorrow night I can get more done



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    Default Re: 4'x8' vacuum table build questions

    Ok so I got the vacuum table all wired up & running but I have an issue. Please read the whole story it's got me stumped.

    I have not gotten the relief valve or vacuum gauge installed yet ( I'm still waiting on the relief valve)

    Once I got the system running I sat the spoil boards in their location and tested the motors. With 2 motors running and all 4 zones open I could not move any of the 4 the spoilboards. So I set up the surfacing file and to be safe I started surfacing using 3 motors. Everything was going great except the dust collector wasn't picking up very well & I wasn't sure why. My wife asked if I thought the vacuum was drawing so much that it was keeping the dust collector from picking all of the dust up. It kind of made sense so I turned off 1 of the 3 motors & instantly the table lost vacuum (this so happened to also be on the last pass of the surfacing file) so I immediately stopped the job. All is pretty much ok except the corner of the one spoil board was cut a little deep but I think it will be ok once it is glued down. But anyhow back to the issue. So I now have everything turned off. So i started trying to trouble shoot i turned on all 4 motors & all 4 zones = NO VACUUM. so I turned off one of the zones (3 on) = NO VACUUM, again turned off a zone (2 on) = NO VACUUM, finally turned off a zone (only 1 on) = NO VACUUM. UGH!!!!!
    I tried each motor & each zone = NO VACUUM. One time the vacuum pulled the spoil board down but just for a few seconds then lost vacuum & popped up. I'm so stumped on this.

    Any help is greatly appreciated
    Thank you
    Gary



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    Default Re: 4'x8' vacuum table build questions

    Can you check the plumbing to see if it is leak free?I really hope that by turning off one of your motors the loss of vacuum didn't allow dust and debris into the pumps.Can you access the intake to see if the pump looks clean or contaminated?One of the machines I ran in the past had a filter upstream of the pump and every year or two we took out the filter element and blew the dust off it.There wasn't much of it as it only got there if we gouged the spoilboard but it was good to know it was prevented from entering the mechanism.

    By the way-gluing a spoilboard down will make your life difficult when it needs replacing.You will have to machine the whole thing into oblivion and guess where gravity will take the dust........



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    Default Re: 4'x8' vacuum table build questions

    Those shut off valves since I am sure they are made for pressure, is it possible the vacuum could have distorted the sealing rings inside?

    Motor vanes packed with dust and chips, pull each and insp?

    Can you run just one motor on the entire table surface and test entire surface with a sheet of paper or thin flat board?

    What I am thinking is perhaps with one motor running it starts the other turning or free wheeling backwards and it starts to run backwards. Happens all the time on HVAC single phase fan motors with two or more.

    Motor or fans do not pull the same, not balanced and one is pulling through the other?

    MDF is porous to a vacuum and perhaps with more vacuum negative pressure its loss is too great?

    Retired Master Electrician, HVAC/R Commercial union shop and Lots of hobbies. FLA Saturn 2 4x4 CNC Router


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    Default Re: 4'x8' vacuum table build questions

    Routealot - I tried to check with a match and I didn't find anything but it is tough to really check do you have a better way than using a match? Could I use tape like " Flex Seal tape or the aluminum tape that I used to seal my dust collection? The aluminum tape is hard to keep wrinkle free.

    I never thought about where the debris will go when I surface off all of the spoil board now I'm concerned as to how to mount it. I know I could use brass screws but the raised part of my is pretty small I'd say 5/8" squares and if I would pre-drill the holes I know I'd have debris get to the vacuum pumps.

    Warren at Central Vacuum said I didn't need a filter as long as I have a spoil board. But I did install a Fernco fitting about 3" out of the motor box to help with vibration, so I could get in there to put a filter if needed. Can you recommend a filter? The motors sound fine & they do not sound like they have had debris go through them.

    Also if it was a leak, why would it work then not work then work a couple seconds then loose vacuum. I'm wondering if the LDF spoil board doesn't have enough surface to hold vacuum & is just drawing the vacuum through? It doesn't make sense but I'm just grasping for ideas.

    Thanks for the help does anyone else have any other ideas?



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    Default Re: 4'x8' vacuum table build questions

    WMgeorge - sorry I missed your post before I replied. As far as distortion. Goes I'm sure anything is possible but these are the same gates that Dvid - DGAGE uses and if it was distorted I wouldn't think I would be able to open & close the valves easily, which I can.

    Can I open the Central vacuum motors or are they sealed?

    I will try today to see if a piece of plastic garbage bag or 4mm coroplast will hold down.

    I have a gate on each motor & on each zone so I can run any of the zones or combination of zones any motor or combination of motors. My motor box has 4 sealed compartments (1 for each motor ) so they shouldn't be able to have freewheeling or back pressure.

    I understand about each motor pulling differently & not being balanced and in that case with multiple motor gates open that is definately possible but 1 motor should be able to pull one zone, & the way my plumbing is set up the unbalanced motors should not come into play.

    I'm not sure what you mean by " MDF is porous to a vacuum and perhaps with more vacuum negative pressure its loss is too great? " unless your saying the same as I was thinking about the LDF Bbing to open to hold it down.

    Also I'm using LDF (LOW DENSITY FIBERBOARD) not MDF (MEDIUM DENSITY FIBERBOARD)

    thank you
    Gary



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    Default Re: 4'x8' vacuum table build questions

    You won't need me to tell you that this could be challenging.Each and every joint in the system could be leaking and any one of the motors could be letting air through when switched off.Its also possible that the forces generated by the vacuum caused the joints in your plenum to crack.I would begin by trying to connect one motor to one section of the table directly-with no joints between and see if the force generated will hold a piece of MDF in place.If it does,keep moving the connection along the system until some component reveals itself as the location of the problem.

    Warren at Central vacuum is correct in that you don't need a filter as long as the MDF is intact.If you have a mishap and cut through the spoilboard and I think most of us have done that once in a while-where do you think the debris will be taken?The filter I mentioned in an earlier post was basically a section of steel pipe with a standpipe inside that was led out at the bottom and then went to the vacuum pump.The top of the standpipe held what looked like a good size truck air filter.The air from the router entered at the side,near the top of the pipe and there was a steel lid on a rubber gasket that could be removed by undoing some wingnuts.Every year or two we cleaned the filter.

    The LDF is beyond my experience.I have known a few people who gave the edges of the MDF a good coat of sealer and I would imagine that LDF would take more sealing.It looks as though you are a little way from needing too many references to vacuum relief valves.Best of luck with chasing the problem.



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    Default Re: 4'x8' vacuum table build questions

    Agree, no filter If your pulling a vacuum directly through the MDF but you say LDF so I do not know. Low density meaning more porous or less? All you need to do really is check the vanes or intake of the fan not the motor, my bad. How about the LDF pores plugged with dust? See below.

    You can make a water manometer to test each fan a inch of water column is IWC to convert to Inches of Mercury Absolute if needed to convert that is.

    Posted from a google Search Result:
    A better option to use as a CNC spoilboard is LDF, low-density fibreboard. LDF has a density of between 0.35g/ cm3 and 0.5g/cm3 making it lighter than MDF. Essentially, spoilboards are sacrificial material being used as a base to cut on so that your CNC table is not damaged by the cutting tool. Being a lighter material, LDF offers better suction between the board and the vacuum underneath the table compared to a thicker MDF sheet. Increased suction allows for stability in regards to your cutting material, resulting in more accurate cuts.

    Retired Master Electrician, HVAC/R Commercial union shop and Lots of hobbies. FLA Saturn 2 4x4 CNC Router


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