I decided to try my hand at making custom pivot hardware that's similar to what's on the original chair. I started with a small 150x150x2 plate of brass for the body of the pivots. I used double-sided tape to adhere it to a piece of melamine, which then was clamped to the bed of the CNC.
I played around with feed and speed, but still broke 10 end mills during the cutting process (see the little stub sticking up below). It's not hard to break 1/32" diameter bits in wood, so I'm not surprised that I had breakage. But it was more than I had expected. I was running on the last bit by the time I finished cutting out all four pieces. This was the first time I had tried cutting metal on my CNC.
Hours later:
The 90 deg V-groove is where the side tab will bend up. The groove depth is 1/2 the thickness of the 2mm plate.
The pins are cut from a 3/8" diameter rod. I'm just testing the pin fit here - it slides freely, but without any slop.
I clamped the tab into the vise and bent down the base by hand. I went slowly and checked the angle as I went.
Checking the angle on the backrest stile.
I peened one end of the pin to mushroom it slightly (not visually detectable). It was enough to make the pin snug-up in the hole as it was seated flush with the bracket. This held it in place for soldering.
Liquid flux worked great to get into the cracks, and I used silver solder for the pin and fold.
After a bit of cleanup, they look pretty good.
Time to enlarge the corresponding holes in the arms. I'm happy that I'll have hardware that is more in-keeping with the original chair. Hopefully, my soldering job will hold together. If not, I'll have a word with the fabricator.
pretty good, id say damn good ross ! i only wish i could do this. of course having a cnc and knowing how to use it might help ! ill just live vicariously through you ! 😂
working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.
Surprised you used such a small bit, I'd have been afraid of using anything under 1/4", but your persistence paid off (glad to see you soldered the fold!)
Feeds and speeds are a mystery to me. Not matter what I always worry that I am going too fast to too slow. What feeds and speeds finally worked for your setup?
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
Pottz commented about 16 hours ago pretty good, id say damn good ross ! i only wish i could do this. of course having a cnc and knowing how to use it might help ! ill just live vicariously through you ! 😂
Thanks, Pottz. The CNC is a great tool, even when it's a struggle to get something cut out.
Surprised you used such a small bit, I'd have been afraid of using anything under 1/4", but your persistence paid off (glad to see you soldered the fold!)
Thanks, Splinter. I like the small bit for a few reasons - parts can be closer, less material removed (64 times less for 1/32 compared to 1/4), less tangential force trying to push the work off the double-sided tape. I did try my single 1/16" bit and it broke too. If I were to do this again, I would probably start with a 1/8" and see how it held up.
Dave Polaschek commented about 13 hours ago Nice! I wouldn't have cut the fold at all, just hammered it over in the vise, but I'm much more of a caveman than you are. Very nice solution, though.
Thanks, Dave. I did consider that, but I had no prior experience working brass, and my research indicated that 360 alloy (which I used) was good for machining, but not great for forming. I was afraid that it my snap if I bent the full 2mm thickness. Bending the 1mm crease went fine, though.
Lazyman commented about 13 hours ago Feeds and speeds are a mystery to me. Not matter what I always worry that I am going too fast to too slow. What feeds and speeds finally worked for your setup?
I found a video that suggested 10k rpm, 5 IPM, and .005 depth of cut. After breaking a couple bits, I changed to 11k, 4 IPM, and .004 depth of cut. That seemed to help, but still broke bits. I should have dropped the feed speed even further. Live and learn.
Thanks, Dave. I did consider that, but I had no prior experience working brass, and my research indicated that 360 alloy (which I used) was good for machining, but not great for forming. I was afraid that it my snap if I bent the full 2mm thickness. Bending the 1mm crease went fine, though.
I've bent a lot of various metals over the years, I've gotten away with making 90 degree bends in even 3mm thick brass (though I'm not positive which alloy that was). 360 is pretty high in lead, so I'm pretty sure it'll handle that bend. Just take it slow and work around the bend to mush the metal around enough that you don't get any thin spots.
It seems only fitting that after breaking all those CNC bits that I should break-off a brass screw when mounting the first bracket, even after drilling a pilot hole. I drilled-out the bulk of the stub, so it should be fine. I ordered some silicone bronze screws that are stronger and will semi-match the bracket color. While I'm waiting for the new screws to arrive, I used some steel screws for the test fit.
The pivot holes in the arms need to be enlarged to 3/8". I drilled a 3/8" hole in a scrap of ply to center over the existing holes in the arms. This centers the 3/8" forstner bit for re-drilling the holes by hand.
With the pivot holes re-drilled, I could mount the new hardware to check the fit.
All I remember from my early days was typical brass alloys got harder with the higher alloy number. Low (200's) were good for forming and the higher 300's machined easier and cleaner, but generally are more brittle and don't really like bending. Can't really get sharp 90 degree bends, always has a radius. I think having the "V" groove was an excellent approach.
Thanks, Dave and Splinter. It's good to know there are some members with metalworking experience that I can tap (no pun intended) for future questions. I am glad I used the V groove - it ensured that the bend location was consistent across all of the brackets. But it's nice to know that bending alone is an option.
When I need to drive brass screws into hardwood, I not only drill a pilot hole but I will often also find a comparable steel screw and drive that in first. That expands the hole further and also pre-cuts the treads into the hole so that the brass screw is less likely to break off. A little wax or soap on the screw adds a little extra insurance.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
Hey - you are metalworker as well! These brackets came out stunning. For accurate, repeatable and economical milling in metal all bits below Ø4 mm shold be considered detailing bits and only be used when absolutely nessesary. I am impressed that this was possible with a Ø 0,8 mm (if I got the measurement right) Good metal hardware levitates a lot of great designs and having the option to make them is a luxury. I see a lot of great projects ahead in that regard
"The good chair is a task one is never completely done with" Hans Wegner
I use brass screws for just about everything I make that needs screws. Bought a set of screw extractors a while back, and they're a lot easier than having to move things around to avoid the bits of broken screw stuck in some hardwood.
And yeah, a steel screw first is a good tip. If you have one. And remember before you've already snapped off a brass screw.
Brass is nice, if you really like to "clock" the screw slots and not break any, I've often drilled an oversized pilot so I can drip in a small amount of epoxy and use a flat punch to press in the screws.
Lazyman and Pottz - I had driven a steel screw first to cut the threads, but I think I may not have bottomed-out the pilot hole when driving it. I've heard the wax tip before, but didn't think to do it. Live and learn.
Ty - thanks for the comments and tips. I'll look forward to my next attempt at CNC metal cutting and will see how I fare with a larger bit.
Dave - I also tried a screw extractor, but ended up blowing out the opposite side with the tip of the extractor! It was definitely a comedy of errors.
Splinter - I'll file that technique away for future work.
