Not in need of any metal music recommendations (but am happy to make them), can anyone recommend a place to stress relieve a steel frame after welding?
Also if you have any tips or a price range I’m looking at I’d appreciate it.
I’ve been toying with building another CNC mill frame but simple shapes are only getting me so far, it’d be cool do something more complex with some thick steel plates.
Seems like a bunch of places here https://www.thomasnet.com/northern-texas/heat-treating-services-37380805-1.html
I’m not sure what you are looking for. Traditionally cast iron is the go to for all milling machine bases. It’s granular, it holds excellent tolerance, machines easily, holds oils, and is heavy so it doesn’t move. @delpn told me back in the war says they used concrete because cast iron was scarce and concrete has similar properties.
You can use welded frames but they will never be as rigid. Stress relief only really needs to be done at welds. This can be done using heat from a torch. This is because the high heat used to weld shrinks the steel. If the weld goes all the way around or in a straight line, the shrinkage is uniform. But at the corner of a welded frame it causes the frame to pull inwards. Preheating large pieces o steel using a torch before welding prevents this and also helps penetration. I have a book on welded frames construction if you want to borrow it.
Steel isn’t aluminum, standard mild steel alloy doesn’t need annealing or “heat treatment” like aluminum does. The weld and gap are most critical in steel construction. It only needs heat treat where you weld it.
Tension and compression in steel frames can only be set during the weld. After it is welded, it is very difficult to change those characteristics without additional bracing/strapping.
A friend of mine just built a huge power hammer base. He used 1/2 plate and welded construction. The original towers for these were cast iron, same with the arms.
What’s this book called?
Can’t remember if i saw this video on talk or somewhere else:
I’d love to use cast iron but that’s no longer a DIY option. There are some cast frames available on AliExpress and similar, but I haven’t found anything I really like.
So as far as rigidity it’d just have to be to make due with what I can. Steel will still be more rigid than doing something aluminum extrusion based. Other option would be epoxy granite, which may be easiest and just lay in some mounting plates to surface on the mill after.
If you have the book (or at least the title to look up) that’d be interesting to take a look at. Everything I’m seeing regarding stress relieving deals with very long term cool downs. There’s ASME specs for Post Weld Heat Treatment, but all the stuff I’ve been able to find relates to air tanks and nothing specific to any kind of machine frame.
the current fad is to grease the bolts, cap the ends of a tube, and then fill the tube with non-shrink grout. It’s supposed to increase the damping because the steel by itself has a lot of ringing. But, it sounds like you’re using plates and not structural rectangular tubes.
The issue with epoxy granite is that you’ll have to put some effort into getting a homogenous mixture, even if you just use play sand rather than more specialized particles
Yeah, my current mill is a PrintNC style (steel 1/4" wall structural square tubes) with a granite gravel + sand + epoxy mixture. There’s some neat papers on damping I’ve seen, but otherwise I can’t speak to any difference as I never had one without EG fill. There was a noticeable difference in the tubes themselves post-fill, they sound more like plastic when you tap them with a hammer. Now I wish I did some lazy bending tests just to see if it did ANYTHING at all for strength, but I doubt it.
This is the book I have. There is another interesting one on weldments by the same author. This one goes into depth from a physics perspective. Center of mass/cross sectional area…ect. If I didn’t have the engineering background that I have in statics…,it would have been much more difficult for me to understand the equations. But if you have the background already it reads like a statics textbook but much more focused on steel I-beam construction
Max,
A phenomenal resource. Thank you for posting this.
Best,
Jim
This all sent me down a couple really good rabbit holes trying to find a good source for details on stress relieving welded steel machine frames, figured I would share some good ones:
Principles and Techniques for Designing Precision Machines:
University of Utah ME EN 7960 - Precision Machine Design:
https://my.mech.utah.edu/~me7960/lectures.html
Foundations of Mechanical Accuracy (old book someone recommended):
I still wanna find “Precision Machine Design” by Alexander Slocum, it seems to be THE reference.
Regardless, I might try picking a couple places off that list I shared earlier and seeing if they’ll even talk/quote, but at this point it may be easier and more interesting to scratch the itch to build a full epoxy granite machine with some cast-in components, either just bearing surfaces or maybe a frame for support.
Thanks for the help everyone!
Have you looked into shot peening yet?
I am curious to know more about your epoxy granite process. What type of resin did you use? How did you get the resin to mix into the particles, and did you have any issues with exotherm? Did you document it or have you any pictures?
I’ve dabbled with compression molding chopped-tow carbon fiber, but it was only a tiny part (and most of it stayed stuck to the mold).
In theory the epoxy by itself can’t contribute much to the flexural modulus of the beam. Just like 3d printing filament, it would get stiffer as you add filler, but steel itself is very, very stiff. You would need continuous fiber reinforcement or a very dry mixture, to get within an order of magnitude of steel.
I’m still a milling babby so I can’t really differentiate harmonic effects from frame damping vs. feeds and speeds. Most of my parts just have adaptive clearing toolmarks with no finishing pass.
Sorry, been busy and forgot to check back here- I haven’t done a ton of reading into it but what I’ve seen is you’re kinda fighting one stress with another- counteracting the inner stress of the weld by putting stress out the outside. It seems like it’d help but in the end I would still have the stresses in the metal.
Sorry, have been busy and forgot to check back here, I’ll try to grab some pictures I took along the way and make a new post. Long story short- I used west 105/206 (regular resin and slow cure hardener), pool sand, and granite pea gravel (it’s sold as Poultry Grit for chickens lol). I called west systems and there was a worry about it going exotherm but my goal percentage of epoxy was roughly 15%, so while it was a pretty thick section (roughly a 2.25" x 2.25" square ranging from 19" to 25" long) the thought was there wouldn’t be enough epoxy there to cause issues. Plus the thermal mass of the fill and the 1/4" thick steel tubes.
I made up a recipe to measure out the dry parts by weight then mixed epoxy then added dry to epoxy. All my steel pieces were pre-drilled so I 3d printed some plugs and covered them in tuck tape sprayed with mold release, which were hot glued in. Not really much more to it, I think I was doing it in roughly 2kg batches, I’d fill up the tubes as much as I could and just mix up another batch of epoxy as needed, which should’ve been within the wet window for the epoxy. All pours were done in the garage last January, I wanna say temps were roughly 60f which probably helped guard against going exothermic as well.
