I have nearly completed my mpcnc and i was wondering…how much pressure is the material getting placed on it? I have seen different methods of holding the material to the table…clamps, bolted down, etc. I have even seen someone just use a hot glue gun. Any advice on what is best to use? If all you need is a hot glue gun i don’t see the necessity for the elaborate hold downs some people are using. Thanks in advance.
Lots and lots of options depending on what you are doing. Hot glue would probably not be best if you wanted dimensional accuracy as the glue would add various thicknesses to the bottom of the work surface. Look up super glue and painters tape on google as a hold down strategy, apparently it works pretty good for some applications and is a rather novel approach in my opinion. Neither of those would be appropriate for aluminum, though, you would quickly be propelling large chunks of material. Also, application/removal time is a consideration. Clamps are easy to reposition and leave no residue. So, different strokes for different folks as they say.
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I use screws a lot. Most of the forces are side to side. Only the thinnest of materials will try to lift. I really depends. I am pretty against all the crazy stuff people spend so much time and money on for hold downs. Each material is very different. I will be trying something new for this next build so we’ll see.
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You just put screws beside the material into the spoil board?
I have done that with wide head lath screws. Or you can just screw directly through the material if you are cutting something out of the center.
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I recently went to screwed-in blocks.
I have 4 blocks of wood with large wood screws in them. I put one on each side of the material I’m holding. With them being mostly wood, if I screw up a jog, it’ll just cut through the block.
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awesome thanks!
The hot glue is placed on the edges where the part meets the spoil board on blue tape. like with super glue only not under because it is to viscus to sit flat. It makes a mess on a end mill though very hard to clean off but softer than a screw.
I still use good ol screws and scrap material for hold downs. I have always wanted to do this however…
Neil
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That looks like what i need also super idea plus a good project
The spoil board looks like a lot of work but I like the clamps. I will have to build some for t-tracks
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I thought about T-tracks, but then was concerned about running the end mill into one.
Another option I thought of is to just get a T-track bit for my router and cut a bunch of perpendicular grooves through the spoil board. I haven’t done this yet to see if it really works or not.
I use 5/8 t-tracks with 3/4 spoil board so I have 1/8 clearance. The spoil board is 3/4 shelving cut 5" wide
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For what it’s worth, it seems painter’s tape and super glue works quite well with aluminium, at least NYCNC on Youtube posted that video on February and keep using it since with at least some of their aluminium milling.
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I’m generally using screws, basically just screwing through the material to the spoil board. But I don’t really recommend doing it this way, it is relatively ok most of the time, but it introduces a bit of warping on the material plate because screws pressure is irregular, and it gets even worse after a few passes or whenever the job is almost finished and most of the screws aren’t holding the workpiece anymore. It is ok while doing tests, but not really appropriate if you plan to use your CNC often or make precise stuff.
In my opinion, vacuum tables are probably the best, but if you can’t build one then the system Neil proposed in the video hereabove is probably the way to go since it doesn’t actually rely on any pressure being put vertically on the material. Wouldn’t work for thin material though.
I cut t-tracks into my spoil board w/ a t-track bit (told mpcnc to cut the tracks for me so they’d be straight).
Since it’s cut from the spoil board i don’t have to worry about hitting a hard t-slot track, and can re-surface several times before it messes up the track. *still have to make sure i don’t run into the clamps.
The slot fits 1/4" bolts, so I’ve made clamps out of scrap wood + bolts, and from 3d printed clamps.
bit:
http://a.co/5xssWDu
clamp:
[attachment file=57768]
[attachment file=57769]
Holy Cow! I never would have thought that would work, especially with that fly cutter he was using. Thanks for pointing that one out.
I have thought about doing that myself. What kind of material are you using for your spoil board?
I’m a huge fan of the glue and tape method. There are two things I do a lot of with my MPCNC - cutting foam board and cutting thin sheet goods.
For the foam board I use a really cheap and dirty vacuum table made from foam board. It’s been posted elsewhere here (since I won an archim board from Ryan with it) but here’s by build video on the vac table for reference:
https://www.youtube.com/edit?o=U&video_id=tyKDV7OIQQs
But for the rest of what I do I really like the tape and glue. I could use the vac table but it’s not really flat enough and running two vacuums and my router at the same time is a good way to blow the fuse in my shop. (I could probably run the table and chip removal with my big vac and a splitter…but haven’t tried rigging that up yet.)
So for thin sheet goods (acrylic, pvc, ply, polycarbonate, g10, mdf…) I want my vac for keeping down the mess not holding down my work. I used screws at first but with this thin stuff screws just don’t work well because the work won’t stay flat or tends to ride up the bit.
I used carpet tape at first - but it’s expensive, hard to remove, and when you cut into it by accident it really gunks up the bit something awful and is tough to clean off.
Now I mostly use blue tape or plain masking tape. Blue tape seems to work a little bit better - it sticks better AND is easier to remove…which I wouldn’t have expected since they seem like opposites.
For glue I’ve tried couple of options. On smaller stuff super glue works great. I put it on the tape on my spoil board then spray a bit of kicker on the tape on my workpiece. Stick them together and go. Super quick, and holds great - as long as you don’t overlap the tape then things stay flat and level.
For bigger pieces (like the 19" panel I cut today) I use spray adhesive. My hands down favorite is 3M 08088 “General Trim Adhesive” but it’s hard to find and expensive. But it’s easy to control where it sprays and doesn’t make too big of a mess. Next best would be the 3M “Hi Strength 90” which you can find at most local hardware stores. It’s cheaper than the 08088 and easier to find…but has similar spray characteristics…it’s not quite as nice but the lower cost and easier availability generally make it a better choice.
My least favorite spray glue is most people’s favorite. 3M 77. I hate the stuff. I just bought a can of it yesterday because my 90 was almost gone and I figured I’d give it a try again as I hadn’t worked with it for a few years and every time the tape and glue method comes up someone asks if 77 will work.
It will, 77 is plenty strong enough. I did some small 4" x 4" pieces as well as my 6" x 19" panel with it and it held them all great. But man is that stuff a MESS to work with. I detest it. It gets everywhere and makes a sticky nasty mess. It comes out in a much finer spray than 90 or 08088 and doesn’t have a directional nozzle - it sprays in more of a cone than a sheet. It is however cheaper and comes in a bigger can so it’s a much better value. Just - mask off more area than you plan to spray and put some towels over your rails or something to protest from overspray because no matter how careful you are you WILL get overspray with 77.
With any of them you use the same procedure. Put tape on your piece and your spoil board - then put a light coat of glue on both pieces and let it dry for 30-60 seconds. If you touch it and glue comes off on your fingers - it’s still too wet. Once it’s dry and glue won’t come off on your hands it’s ready - just be sure you’ve got things lined up well because as soon as the two parts touch it’s not going anywhere.
FWIW I spent 2 years working part time making suspension seats for off road racing vehicles when my business was having a slow period. My main task was cutting the foam that makes up most of the seat and gluing the layers together We used 08088 most of the time - but occasionally our supplier would run out and we’d have to use 90 or 77. If we only had 77 I’d call in sick I hated working with it so much. 08088 and 90 both clean up fairly easily with cheap citrus adhesive removed we’d get at walmart (I forget the brand name but it was really cheap) - just spray it on, wait a minute, then scrape the glue off with a putty knife.) The 77…nothing softened it up and it took a lot more time and effort to get it off the table no matter what kind of cleaner we tried.
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I don’t normally use that much tape - usually it’s all hidden under the part. But with the 77 I wanted to protect against overspray so pu 2" of tape beyond where I usually would.
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Since this would be an update to Marius’ ultimate clamping solution, thought I’d put this here. I think there are old topics that are still valid.
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