Cyanoacrylate (super-glue) fixturing?

sfriedberg · Nov 20, 2019

We've got a one-off job coming up where we need to reduce the thickness of some stock 0.125" 6061 sheet to 0.098" and also cut some 0.050" to 0.070" slots the majority of the length of the part. My intention is to face off a sacrificial block held in the vise, then super-glue the sheet to the just-cut face, face off the sheet to the required thickness, then switch to a slotting cutter and cut through both the sheet and the sacrificial block. Release would be via industrial heat gun, possibly assisted by some (unheated!) acetone. Incompletely cut ends of the slots (due to slotting cutter diameter) would be finished by hand.

Area of the part is 4 to 5 square inches, so I am not worried about shear. But peeling and impact resistance concern me, especially peeling from the slotting operation which might tend to pull up on the edges of the slot. Am I going to run into trouble if we use a toughened cyanoacrylate like Permabond 731, 735 or 737 (Black Magic)? Could this be done with simple methyl cyanoacrylate like Permabond 910, or am I correct that garden-variety Super-Glue doesn't have the impact resistance to hold up to milling?

Thanks for any experience you can provide.

gusmadison · Nov 20, 2019

The kid at NY CNC on youtube has several videos of their journey sorting through what works and doesn't with those glues. Be sure to look towards their latest video on the subject, as they have kind of made it a mission of constant improvement and he shares freely.

Screwmachine · Nov 20, 2019

I and several folks I know have used Loctite 480 cyanoacrylate (black, rubber reinforced)for years, decades. It's fantastic for holding thin work down where no other fixturing would be practical.

With two flat faces like that acetone would take days or more, heat is your ticket. Heat gun should work, when I need it I use a hotplate on the first setting.

trevj · Nov 20, 2019

All the clock maker videos and books I see that use super glue for fixturing, recommend a series of slots in the base plate, to allow some air to access the middle portions (carries the moisture that 'kicks' the CA glue). It also allows the excess to go somewhere.

Dunno how big your parts are, but would a vacuum plate work? Have seen several variations of that theme. Usually a big rubber o-ring and a checkerboard pattern of grooves to allow the ring to be strung in various directions.

winger · Nov 20, 2019

He is also using tape with superglue.

Dave

garyhlucas · Nov 20, 2019

I think Mitebite sells a heat release tape just for this purpose.

plastikdreams · Nov 20, 2019

I'd be more worried about it becoming a potato chip and breaking the bond.

MrWhoopee · Nov 20, 2019

I would also be concerned about it curling up when released. What's the thickness tolerance? Maybe get some "select" grade 10 gauge.

sfriedberg · Nov 20, 2019

Thickness tolerance is informally +- 0.002". In this particular situation, curling won't be an issue. The finished part will be restrained, and the customer is willing to hand-flatten if it won't initially go in the mating recess. Keeping in mind that we will have to "torch" the part to get it to release from the fixture, asymmetric stress relief due to milling one face is not my biggest concern. :-)

The local Grainger has a bottle of Loctite 480 with my name on it for pickup tomorrow morning. We'll see how this goes.

DMF_TomB · Nov 21, 2019

some use thin double sided foam tape cause it has some flex to it
.
some super glue has some flex to it. but be aware of glueing different metals like steel and aluminum which expand at different rates.
.
had a steel part glued aluminum block slightly warm from milling and took to sink under cold water. they broke or fell apart in my hands from temp change. just saying if glue bond suddenly breaks it can be a problem especially if during machining.
.
thin foam tape like .030" thick will flex more than .001" at times but many times thats much better than bond breaking suddenly.

BugRobotics · Nov 21, 2019

I use Loctite 380 and this tape from Mcmaster: 7630A43. I use these in conjunction with a freshly faced plate and clamps. Surface prep is everything to ensure good tape adhesion. Once you get it right though it's pretty secure. I always try to respect the setup and keep cuts relatively light.

Here are a few shots of a thinner part using this process from a few weeks ago. In this case I used some dowels in the subplate to ensure alignment when flipped which also contributed to the security of the setup.

richard newman · Nov 21, 2019

That's three thickness tolerances stacked up - 2 tape and 1 glue line. What is the typical thickness variation of the finished part?

BugRobotics · Nov 21, 2019

richard newman said:
That's three thickness tolerances stacked up - 2 tape and 1 glue line. What is the typical thickness variation of the finished part?

Great question. The thickness varies 0.0014" over a length of 240mm (~9.45in). Less than 0.0003" over a width of 191.5mm (~7.54in). Certainly not the quickest method as a vacuum plate would be better but for my work, typically one off parts to verify a design for my clients, works pretty good.

rons · Nov 21, 2019

sfriedberg said:
Thanks for any experience you can provide.

Many times I have been disappointed with super glue on bonds with all kinds of materials. The only thing that it does good on is skin, which is what it was originally developed for.

mike 44 · Nov 22, 2019

Hot hide glue. removes with a heat gun. Residue cleans up with hot water . Brush on face plate ,stick part on, or let the glue cool, use heat gun on part to adhere it. I have heard but not tried shellac to adhere thin parts to a face plate. Alcohol is solvent for shellac.
I had to thin 140 brass discs to .025 for a machine shop that did not want to bother with it. I installed an MDF scrap to a 10" face plate. Brushed hot hide glue on, stuck the pieces on and rolled them with a laminate roller while heating them with a heat gun. When faced to dimension the brass came off by heating them and scraping them off. Residue came off with hot water and paper towels.

BugRobotics · Nov 22, 2019

mike 44 said:
Hot hide glue. removes with a heat gun. Residue cleans up with hot water . Brush on face plate ,stick part on, or let the glue cool, use heat gun on part to adhere it. I have heard but not tried shellac to adhere thin parts to a face plate. Alcohol is solvent for shellac.
I had to thin 140 brass discs to .025 for a machine shop that did not want to bother with it. I installed an MDF scrap to a 10" face plate. Brushed hot hide glue on, stuck the pieces on and rolled them with a laminate roller while heating them with a heat gun. When faced to dimension the brass came off by heating them and scraping them off. Residue came off with hot water and paper towels.

Ah, I've never tried hide glue but I'll have to now. Thanks!

tjd10684 · Nov 22, 2019

I have had pretty good luck with carpet tape. I will admit though I have not needed to do anything tighter than +/-0.005

Bluejeep · Nov 23, 2019

I've used the nycnc method. It worked awesome. saved me from making fixturing for a bunch of 1off parts.

corednc · Nov 24, 2019

The tape and superglue method work well but another method that I think works better is to create a slotted fixture, 1/8 slots that go through the fixture so that it looks like a grate with slots running all the way down. Next face off an aluminum plate and place the sheet on the plate then place the slotted fixture on your sheet and use a hot glue gun to inject glue through the slots to the back side of your sheet. You can also just cut up the glue sticks and put the pieces in the slots and put the entire thing in an oven. The hot glue will seep though the slots to the backside of your sheet. This method also allows you to place a weight on the fixture so that there are no air gaps between the fixture and sheet.

So it should look like this
_________________
| Oven |
|_________________|
| |
| Weight |
| Slotted fixture |
| Sheet |
| Faced off plate |
|_________________|

Best parts are no tolerance stack up issues like with the tape and super glue and glue can be reused since gravity will cause remainder to stick to back of next sheet.
Do not use the hot glue you get at Walmart it is very weak compared to normal hot glue. Weak hot glue has its place but this is probably not it.

Cyanoacrylate (super-glue) fixturing?

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