Right now I'm assembling a Triode Electronics Mk3 kit. It uses this chassis:
NEW Upgraded Dynaco Mk3 Stainless Steel Chassis MADE IN USA
They didn't provide screws however for the bottom plate. Attached are images showing that the holes pre-drilled in the chassis are just smaller than a #4 screw similar to what they provided for the sockets, etc. and the holes in the bottom plate are more the size of the provided #8 screw for the transformers.
I'm just wondering what I need to order here. I know vintage Heathkits and probably Dynacos used self tapping sheet metal screws. So far I've been looking at either thread forming (thread rolling) vs. thread cutting. I'm not really sure what the best application is though. It kind of seems like I don't want sheet metal screws though.
Also as part of the confusion, given the different hole sizes, I'm not sure which size I need based on the difference in hole sizes mentioned above between the chassis and bottom plate. I'm guessing probably a #4 screw, seeing how it's about that size. In pictures of other amps I've seen the heads on screws that look to be on the #6 size though, which would be the in-between size in this case. Given that size of hole in the chassis, could a #6 screw be used?
Here's some options I've been looking at so far:
https://www.fastenal.com/products/details/0148284?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600068%20Thread%20Rolling%20Screws%22|~%20~|sattr05:^%229pound6%20-%2032%22$|~%20~|sattr04:^Phillips$|~%20~|sattr10:^3/8%22$|~
https://www.fastenal.com/products/details/0148280?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600068%20Thread%20Rolling%20Screws%22|~%20~|sattr05:^%229pound4%20-%2040%22$|~%20~|sattr04:^Phillips$|~%20~|sattr10:^3/8%22$|~
https://www.fastenal.com/products/details/32251?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600067%20Thread%20Cutting%20Screws%22|~%20~|sattr05:^%229pound4%20-%2040%22$|~%20~|sattr06:^3/8%22$|~%20~|sattr03:^Pan$|~%20~|sattr04:^Phillips$|~
https://www.fastenal.com/products/details/0173553?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600067%20Thread%20Cutting%20Screws%22|~%20~|sattr04:^Phillips$|~%20~|sattr03:^Pan$|~%20~|sattr05:^%229pound6%20-%2032%22$|~%20~|sattr06:^3/8%22$|~
Not really sure what the Triode folks intended or what the best solution is.
Thanks!
NEW Upgraded Dynaco Mk3 Stainless Steel Chassis MADE IN USA
They didn't provide screws however for the bottom plate. Attached are images showing that the holes pre-drilled in the chassis are just smaller than a #4 screw similar to what they provided for the sockets, etc. and the holes in the bottom plate are more the size of the provided #8 screw for the transformers.
I'm just wondering what I need to order here. I know vintage Heathkits and probably Dynacos used self tapping sheet metal screws. So far I've been looking at either thread forming (thread rolling) vs. thread cutting. I'm not really sure what the best application is though. It kind of seems like I don't want sheet metal screws though.
Also as part of the confusion, given the different hole sizes, I'm not sure which size I need based on the difference in hole sizes mentioned above between the chassis and bottom plate. I'm guessing probably a #4 screw, seeing how it's about that size. In pictures of other amps I've seen the heads on screws that look to be on the #6 size though, which would be the in-between size in this case. Given that size of hole in the chassis, could a #6 screw be used?
Here's some options I've been looking at so far:
https://www.fastenal.com/products/details/0148284?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600068%20Thread%20Rolling%20Screws%22|~%20~|sattr05:^%229pound6%20-%2032%22$|~%20~|sattr04:^Phillips$|~%20~|sattr10:^3/8%22$|~
https://www.fastenal.com/products/details/0148280?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600068%20Thread%20Rolling%20Screws%22|~%20~|sattr05:^%229pound4%20-%2040%22$|~%20~|sattr04:^Phillips$|~%20~|sattr10:^3/8%22$|~
https://www.fastenal.com/products/details/32251?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600067%20Thread%20Cutting%20Screws%22|~%20~|sattr05:^%229pound4%20-%2040%22$|~%20~|sattr06:^3/8%22$|~%20~|sattr03:^Pan$|~%20~|sattr04:^Phillips$|~
https://www.fastenal.com/products/details/0173553?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600051%20Screws%22|~%20~|categoryl3:%22600067%20Thread%20Cutting%20Screws%22|~%20~|sattr04:^Phillips$|~%20~|sattr03:^Pan$|~%20~|sattr05:^%229pound6%20-%2032%22$|~%20~|sattr06:^3/8%22$|~
Not really sure what the Triode folks intended or what the best solution is.
Thanks!
Attachments
Sure they are. you could use self gripping nuts sometimes called press fitting nuts. McMaster has them. I'd use the zinc plated steel type in whatever size is closest. You might want to drill out to the best fit once you have them.
No special tool needed. With the proper size hole I just use a bolt, and washer if needed, to draw the captive nut into the metal.
Sometimes a vice grip pliers will work if there is room to fit.
edit: Don't you love how these posts get moved around without any mention of where they went. I had to back page to find it!
Sometimes a vice grip pliers will work if there is room to fit.
edit: Don't you love how these posts get moved around without any mention of where they went. I had to back page to find it!
Last edited:
I love things like PEM nuts, but they're not easy for the average person to install, especially in stainless steel. I'd probably tap the holes for regular #4 or #6 machine screws, redrilling with the right size tap drill if necessary. Use lube! Don't use stainless steel screws for a stainless steel chassis, as they can gall and seize.
Everything that Conrad said, Pem nuts require a press to insert in stainless so that is out. I would measure the exact diameter of the hole and see what you need to do to tap it. Use good quality taps, not the junk from Home Depot or Sears. Look for an industrial supply house that sells to machine shops. For what the chassis cost, they should have been tapped already, I think someone missed a step in the manufacturing process.
BillWojo
BillWojo
Bill,
I was able to determine that they were almost a 3mm hole to start with, basically equivalent to a #36 or #35 drill hole. From there I just used a 6-32 tap and everything worked out fine. I ended up using button head hex screws for mounting sockets, etc. and so used stainless 6-32 screws here as well and they fit nice.
It does kind of make me wonder if the old chassis for heathtkit and dynaco were pre-tapped for sheet metal screws as they provided with their kits in the past (versus machine screws I've used here). I've tried looking at manuals for an aa-151 and various dynaco amps and they don't really mention anything other than "use the provided screws based on pictorial 1".
Kevin over at Dynakitparts also had the same advice for me regarding this issue and helped guide me towards this as a solution. He had mentioned the chassis he gets fabricated have their holes pre-tapped right during the process also using a 6-32 tap. This would hint at using more of a machine screw vs the more coarse sheet metal screws being provided with the original vintage amp kits.
I was able to determine that they were almost a 3mm hole to start with, basically equivalent to a #36 or #35 drill hole. From there I just used a 6-32 tap and everything worked out fine. I ended up using button head hex screws for mounting sockets, etc. and so used stainless 6-32 screws here as well and they fit nice.
It does kind of make me wonder if the old chassis for heathtkit and dynaco were pre-tapped for sheet metal screws as they provided with their kits in the past (versus machine screws I've used here). I've tried looking at manuals for an aa-151 and various dynaco amps and they don't really mention anything other than "use the provided screws based on pictorial 1".
Kevin over at Dynakitparts also had the same advice for me regarding this issue and helped guide me towards this as a solution. He had mentioned the chassis he gets fabricated have their holes pre-tapped right during the process also using a 6-32 tap. This would hint at using more of a machine screw vs the more coarse sheet metal screws being provided with the original vintage amp kits.
Glad it worked out for you. Be careful about using stainless steel screws in stainless as they can cold weld together or gall. In industrial applications where all stainless must be used it is common to use a antiseize compound on the bolts so they don't seize up when it is serviced. Even than it can be a problem.
BillWojo
BillWojo
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