Gluing steel to a milling fixture

S

Sandow

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Jun 13, 2013
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So I'm fairly new to both machining and knife making but I was working on an aluminum fixture for a knife I am going to mill the flats of and it occurred to me that rather than screwing my steel billet to the fixture, I could simply glue it in place. Wasn't sure if it would actually hold up and I have yet to see anyone mention doing it, so I did a test run with some scrap.

I drilled out the aluminum to accommodate a 3/8 grade 8 bolt so I could easily fit it to the table with a T-nut then faced the fixture at a low but random angle.

https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;6C140A44-838A-4031-B213-39CD490C4E32
https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;BB25CAC0-875D-4E47-9AB6-DCCC87FFDD18

Super glued a bit of cpm 154 to the fixture... evidently to intoxicated to remember to bolt the fixture down to the table first though...
https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;F09D6B23-9FC9-4843-8136-310BC9D60287

Wasn't sure if this was going to break loose so a few passes from an old chewed up mill later...
https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;A1227252-4A72-4106-A60E-31A513C6BA1D

A few passes with a heat gun and the glue melts (MP for CA is ~ 368F) and the steel pops off.
https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;31C48EF7-D42C-4DB7-8729-3E1C0CD76155

I ran out of acetone to clear off the residue, but that would get you back to clean bare metal in short order. Given that I only gave this 5 minutes to cure and it was about the worst case scenario in terms of surface area bonded. This seems like a pretty painless way to stick a workpiece to a fixture but in searches I never see it mentioned. Am I missing something?
https://www.icloud.com/photostream/#A1JtdOXmJuDrvD;6F3B154F-8948-43C3-BF69-081462713D7E

Nathan, I'm looking at you here ;)

-Sandow
 
it would not be a good idea with a lager piece of metal that could fly off and cause injury/damage if you approached the cut too deep.
It may have worked for you this time but that dosent mean it will always work or that its the correct way to do things.

if you are trying to mill that bit of steel thinner that you have glued to the top, then you should have blocks in your vice that will hold the material at the right height from underneath for you to mill the faces.

or use clamps like this
drilling_lanyard_holefea.jpg
 
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Wondered about that too but at 2,500 psi even one square inch of superglue exceeds the maximum torque from a 3 hp motor by 800%. By comparison, magnetic fixtures are way lower in holding force than this. If I needed more strength I could step up to epoxy and hit 4000+ psi and still have a glue that could be melted off.

-Sandow
 
Magnetic fixtures are constant, with no variables such as surface preparation, time left to set etc.

If i had to choose to hang off an object, or trust my safety to an object that was held in place with either a mechanical fixture (clamp), an electromagnet, or superglue I sure know which one i would not choose.

No offence, but as someone with some experience in this field I can only see several reasons why someone would pick to glue it over any of the tried, tested and accepted industry methods.
A. because they either don't know how to do it properly, B. they don't have the tools to do it properly C. Don't have the patience to set up the job properly. (none of which are an insult)


Anyway, you did it and all is good so that's great. The piece of metal you did it with could probably do minimal damage at best if it flew off somewhere. Im just pointing out that glue is by no means best practice in engineering.
 
There are a lot of hidden dangers in machining, so people lacking a great deal of experience are frequently better off sticking to tried and true methods to minimize their risk. When venturing out of your safety zone one needs to work slowly and keep asking the question "what if".

I consider myself inexperienced with a buffer, so I made myself a polycarbonate apron to cover some of my favorite bits, just in case...

Machining parts retained with glue is not conventional, but I believe this is due more to the fact that appropriate machinable adhesives have not always been common and inexpensive. People have been machining off two sided tape for a long time. Super glue was something like $.25 a drop when it first came out.



(the damn website software won't let me post my full reply. let me try and do it in pieces here)
 
I machine off of adhesives all the time. There are parts I make where it is the only good way to achieve the results that I want. It is the only way to hold a part where you can cut 5 out of 6 sides without inducing stress into a large thin part. I make large aluminum plates that are machined truly flat. The fist side I use epoxy, then when I flip it over I can use vacuum.

Super glue works well, but it is slow to set inside the joint where it doesn't have access to moist air, which can leave you with less bond than you think. I like it because it can be wicked into a joint, but I like certain epoxy better because it is more reliable and has easier clean up.

My favorite epoxy for this is the big bottles of consumer grade 5 min loctite epoxy you can buy at places like Lowes. They cure fast, they're not gummy to machine, and they always have consistent, repeatable poor bond strength. The epoxy is rubberized so clean up consists of pealing it off your parts where its poor adhesion allows it to pull off cleanly. Kinda like a stick-it note.

(aside) you never want to use this grade of stuff for knife making, by the way...

I usually only use small cutters when profiling. If something does go wrong, an 1/8" cutter simply can not launch a part at highly dangerous speeds. In all my years of doing this, I've never had a part "launch" more than a few inches.

When milling the top surface of steel, you will induce stress into the skin of the part that will make it draw away from the cut. When you pop it off, it will not be straight. There are methods for dealing with this.

Don't think for a second that once square inch of bond is enough to stall a 3 HP spindle. The math aside, is simply isn't.
 
So, anyhoo, epoxied work piece being machined:

9.jpg


The mostly finished part

10.jpg


Machined on all five surfaces (this was all done very quickly, by the way)

11.jpg
 
Heh... I won't deny for a second that I'm as lazy as I can get away with. I actually have a proper fixture already made for what I need to do. It was only while I was considering the limitations of bolting the workpiece by both ends that I thought about gluing it in place.

Searched around a bit more and nihil novi sub sole... Though these guys are using dots of optically setting and releasing glue rather than using thermal release.
http://www.mmsonline.com/articles/light-activated-glue-holds-and-releases-workpieces-in-a-flash

not sure what is with the russian techno...
https://www.youtube.com/watch?v=axS-CjLoIPA

Slides in engrish about the process:
http://www.mts-rnd.com/app/galery5e.asp?f=maz

They are saying 300 to 450 kg/cm2 in depending on where you look which translates to 4300 to 6400 psi. Easy enough to get into that range with epoxy though cleaning up the residue is way worse than for CA.

The safety concerns are legitimate of course. Having a knife chucked at you is hardly ever fun. I'll glue some larger pieces to my current fixture and use the bolts a slightly offset so they provide a safety catch if the glue gives up the ghost and see how it goes.

-Sandow
 
I appreciate the reply Nathan. When you have had pieces break loose, what was the cause?

Also, since the bond is likely to be strictly mechanical with these glues, is it worth roughing the fixture surface slightly rather than leaving it with a smooth machined finish? Was kinda thinking a few light passes in the sandblasting cabinet might help things without much dimensional change.

-Sandow
 
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Nathan,
I really appreciate all the help and advice you give us novice machine users,I've learned a great deal from your posts.
I don't intend to hijack this thread but wondered if you would answer in another thread about how to deal with the stresses in steel that cause it to draw away from the cut and end up being warped. Is there a way to prevent this or to minimalise this or is the only solution to bend it back straight afterward?
 
Sandow said:
I appreciate the reply Nathan. When you have had pieces break loose, what was the cause?

Also, since the bond is likely to be strictly mechanical with these glues, is it worth roughing the fixture surface slightly rather than leaving it with a smooth machined finish? Was kinda thinking a few light passes in the sandblasting cabinet might help things without much dimensional change.

-Sandow
Click to expand...

You should be face milling your fixture flat before use anyway. That leaves plenty of tooth. I clean the fixture with acetone and simply wipe my part clean with a coolant soaked rag, so the glue stays stuck to the fixture upon release rather than the part.
 
Calvin Robinson said:
Nathan,
I really appreciate all the help and advice you give us novice machine users,I've learned a great deal from your posts.
I don't intend to hijack this thread but wondered if you would answer in another thread about how to deal with the stresses in steel that cause it to draw away from the cut and end up being warped. Is there a way to prevent this or to minimalise this or is the only solution to bend it back straight afterward?
Click to expand...

A sharp cutter and a relatively light depth of cut and a healthy chip load per tooth will minimize the distortion.

Heating it to a sub critical anneal will often straighten it.

You should not bend the part back straight if it is a knife blade. It is distorting because the surface is slightly smeared, putting it into compression. It is just in the skin. If you bend it back straight you'll have stress across the entire section. What will happen is the skin will relax during heat treat canceling out that part of the stress and the part will bend back the other direction.

I deal with this by machining the first side clamped in a vise in a relaxed state. Then flip it over and spring the part flat and clamp it in the vise and cut it again. The two stress generally cancel each other out. You'll want to tap on it with a hammer to fully seat it against the parallels before cutting on it.

I've milled many knife blades this way and they almost always turn out straight after heat treat.
 
To be brutally honest, when I first opened this thread I thought it was going to leave me like this--- :eek: :confused: LOL

But it has turned out to be really interesting. Thanks guys! :)

I'm not sure about only using small cutters and light cuts. I routinely fixture damascus billets to the Cincinnati with a hot glue gun and take 0.200" per pass to clean up forging scale....


;) Just kidding, and please don't try that! LMAO

Thanks for all the info and pics Nathan! :)
 
NickWheeler said:
I'm not sure about only using small cutters and light cuts. I routinely fixture damascus billets to the Cincinnati with a hot glue gun and take 0.200" per pass to clean up forging scale....


;) Just kidding, and please don't try that! LMAO

Thanks for all the info and pics Nathan! :)
Click to expand...

I'm going to put my one try milling wire damascus right up with the first and last time I try machining 316 lol.

-Sandow
 
NickWheeler said:
To be brutally honest, when I first opened this thread I thought it was going to leave me like this--- :eek: :confused: LOL

But it has turned out to be really interesting. Thanks guys! :)

I'm not sure about only using small cutters and light cuts. I routinely fixture damascus billets to the Cincinnati with a hot glue gun and take 0.200" per pass to clean up forging scale....


;) Just kidding, and please don't try that! LMAO

Thanks for all the info and pics Nathan! :)
Click to expand...


:eek:

Oh I actually do routinely use a 3" face mill with just glue and take 5 HP cuts. With large glue surface area and inside a full enclosure. However I don't particularly recommend it.
 
So I made a gluing plate with some reliefs to aid in setting super glue across such a large area.
http://www.flickr.com/photos/98126710@N08/9143988731/

Glued a damascus billet to it and gave it a day to set up. Face milled it taking off about .002" per pass and was reasonably happy with the was most of it cut. Last time I tried milling it the lockup wasn't nearly as solid as the glue and it was skating and chattering. It is clear that there are places where the layers were not completely bonded though.
http://www.flickr.com/photos/98126710@N08/9146212682/

I got this as a random christmas gift and have no idea what metal was even used. I'm assuming this is B stock that someone wasn't happy with for their own use. Is this just scrap or is it possible to fill these imperfections? The poorly bonded sections are all toward the middle and the material where the blade edge would be seems solid.

Hmm... really doesn't want to imbed my images.
-Sandow
 
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One BIG consideration in gluing things for milling/turning is the way the joint may fail. Double sided tape and super glue will hold things well if they will only get downward pressure or other direct stress. If the force will be a shearing force, Super glue may break away, but the tape will hold pretty well. If there will be heat built up in the milling/turning, then the super glue will fail quickly as it approaches about 200F. The tape will give away a little sooner.
 
Yeah, I built a cage around it while I was cutting in case it broke away. Was concerned about the temps since I was cutting more or less dry but the surface temp after passing over an area seemed not to have changed. Was throwing blue chips too so I expected noticeable warming but it was either bleeding heat off in the chips themselves or it was being conducted fast enough through the aluminum that I couldn't tell. My speeds and feeds were pretty modest anyway.

Did wonder in the glue vs tape if the tape would be better because of its tendency for ductile failure. Might give you more warning than the CA. I tried the flexible epoxy on a small scale but found it much harder to separate the pieces and remove the residue. The stuff I used set up fairly hard though, maybe I need to try the loctite that Nathan recommended.

Any opinion on rescuing the flawed damascus Stacy?

-Sandow
 
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