Dane Lance

Ah, timgunn, thank you! That puts it all in perfect perspective. I was ignoring the voltage variance by the VFD vs amps in the sub-60Hz range. I understood it concerning the base+ speeds. The trade off between the two different motors then, is that the 4-pole will have more torque in the sub-60Hz up to base speed, but lose in the torque department to the 2-pole beyond 75Hz. The 4-pole does provide a broader speed range, 900RPM to 4500RPM (30Hz to 135Hz), theoretically that is, if balance is the only limiting factor and what I read about manufacturer balancing holds true. The 2-pole speed range would only manage 1800PM to 4500RPM (30Hz to 75Hz). Additionally, the 4-pole has less torque in the upper range, but more in the lower range. Almost seems opposite of what I really want. If frequency were theoretically unlimited in a motor, then at some point beyond base speed, the motor will not be able to increase RPM once torque falls to that necessary to simply keep the motor (or the entire device it is attached to) turning as long as amperage remains constant and only frequency is increasing. I get torque and RPM, at least as it applies to HP in reciprocating engines, things get a bit funkier with electric motors and even more so with a VFD. Will the AC motor operate the same on the VFD as far as back EMF and sync? What I mean is, with no load, back EMF acts like an amperage throttle, so no load is less amp draw and synchronous, or near synchronous RPM. Add a load, RPM drops, back EMF decreases, which allows more amps, motor makes more torque to try to get back to rated RPM. This is more like a constant speed mode. This is why it's often said you can replace a gas engine of a given HP with an electric motor of lesser rated HP. In practice, however, you can get away with it only for intermittent use. Continuous duty cycle needs a 1 to 1 swap. Or, do 3-phase motors act differently than this? Or better yet, just find out what everyone else uses and steer in that direction. This is making my brain squirm too much this morning.

Yeah, I'm probably overthinking things, I usually do, mainly because the cost of a VFD and a motor isn't chump change and I want to make sure I get the "right" set up...plus learning new stuff is always good. An inverter rated motor is a definite (I've learned about that already). Something else I learned, or at least read about...both 2-pole and 4-pole motors are typically balanced to speeds of 25% over base of the 2-poles, meaning both are balanced to about 4500RPM. On a VFD, this equates to 75Hz on the 2-pole and 135Hz on the 4-pole. Assuming the correct VFD, theoretically, the 4-pole motor is going to give you the widest speed range, but does running it at sub-60Hz ranges create too much heat? (more torque for same RPM means more power). The question is, how much more? Inefficiencies considered, I would guestimate it has to be something over twice as much, but is it verging on burning up the motor, or is it within tolerances?

Most of the wheel sets I'm seeing are 4" drive wheels. I'll go with the 3450/3600 RPM inverter duty motor. 3450 RPM with a 4" wheel is around 3600 SFPM. Assuming the motor will be ok and the KBAC VFD I'm looking at will do it, 30% of max speed is about where I figure the low end will be, so around 1000 SFPM. I should be able to run the motor above max speed with the VFD too so, actual top speed should probably, safely, be somewhere around 25-30% over max as long as the VFD can maintain the V/f ratio. This would get things in the 4300-4500 RPM range on the high end without cooking stuff. I think that's a nice and useful speed range. I've seen grinders running in the mid 5,000 speed range, if not closer to 6,000 and that seemed a bit much, if not scary.

Before I go all crazy and start welding up steel to make a Jeremy Schmidt grinder, I have a couple questions concerning VFD's and AC motors that maybe someone can shed some light on. I understand the basics of how they work, that I need a 3-phase motor and all that, but I'm not so clear on what I really need in terms of powering my grinder, or more specifically the "mode" of operation. With a VFD you can run variable torque, constant torque, and constant HP, etc. From reading it seems a constant HP mode would be best for a grinder (at least all the charts I've found say that). But, it seems from further reading, that a "constant HP" mode is only achievable when running the motor above base RPM. Essentially, you get two modes with the set up, "constant torque" which occurs for speeds from 0 to base RPM, then constant HP when running above base RPM. Constant HP is achieved by varying the voltage once speed passes base. So, I guess the question is, do I go with a slower base speed motor (like a 1750 RPM), size the drive wheel such that base RPM at the motor is my "slowest speed" on the grinder, then drive it up from there? Or, is all of this not really needed and just run it in constant torque mode (i.e. at or slower than base RPM) and not worry about it? Seems running at slower than base RPM for any length of time will cause a lot of heat build up and not be good for the motor?

Yeah, that's the only video of his I've ever seen him use that tuning fork, maybe there's some humor there that I just didn't get. I like his stuff, he makes some really nice patterns and manages to make some nice looking stuff from all sorts of random metal pieces.

He didn't hit the fork during the quench, he did it while he was heating the blade to quench temp. As if he would get a certain tone when the blade was at the right temp.

I pretty much thought this was some hokus pokus, but just never seen it before. I know about the north south thing and had a bit of a chuckle the first time I heard about that. Lol, it's entertaining, if nothing else.

I've watched quite a few videos by a Russian fella on youtube (channel name: shurap). Guy makes some crazy good looking damascus from all sorts of stuff, but in one particular video where he's making "dragon breath" damascus, during the heat treat, he is holding the blade in a long holder that has a tuning fork on the end. Right before he pulls the blade out of the forge, he strikes the tuning fork. I assume this is some method of determining the blade's temperature for heat treat? I've never seen that before. Here's the video. You can jump to the heat treat at the 8:00 mark:

Good point, I hadn't considered forging to shape might be an issue.

Makes perfect sense. Sounds like it's a little tedious with having to seal things up to prevent chromium oxide. And yes, a san-mai construction is what I've seen. Carbon migration looks to be visible in the region where the two metals are welded and the bevels ground on the blade (and that is part of what makes them look so nice). It would also seem that the right flavor of stainless is needed too. I looked at some coefficients of linear thermal expansion for carbon and stainless steels. While the plain chromium grades have similar CTE values as carbon steels, the austenitic grades are around 1.5 times higher. Also, thermal conductivity for stainless is a bit less than carbon steel, so that could be a big problem with warping or cracking during a quench. I could see the carbon steel core possibly pulling completely loose or maybe even splitting. I'd say an edge quench would be the way to go. However, even with what sounds like a recipe for doom, some folks are doing it and making some awesome looking knives. Lol, I guess there's a couple ways to go about this...read more, see what other info I can find...or just go try it!

Did some looking here, but haven't found much. Did some looking on youtube as well and there are a couple of videos of some folks successfully forging stainless to high carbon, but not much on the actual process or how they did it. Anyone here do it? Is it terribly difficult? Are there any benefits to it? I'm kind of more curious about it than anything. The examples I've seen made for some beautiful knives.

Couple possibilities: Round the finger area with the heel still swept back some, also a slight drop to the tip: Or, continue the finger round down along the heel and a slightly more aggressive drop on the tip:

"San" in Japanese is "3." "Go" is "5." Shino-Japanese 1 to 10: Ichi - 1 Ni - 2 San - 3 Shi - 4 Go - 5 Roku - 6 Shichi - 7 Hachi - 8 Ku - 9 Juu - 10 "Mai" is Japanese for "sheet." In terms of knife making or billet making, we'd probably translate it more as "layer." But, more or less the same thing. So, "San-mai" is "3 sheet", "Go-mai" is "5 sheet", etc.

Ok, when I get a chance, I'll bust out the lens and do some pics of metal sanded with various grits. Kinda doing a major clean up/rearrange of the wood shop right now and have some hand tools that got a little rusty and need to get them cleaned up.

Honorable mention It's more than just a piece of thread....