aarongough
Stainless
- Joined
- Oct 27, 2014
- Location
- Toronto, Canada
Hey All!
I have been considering wire EDM for part of my production process for a few years, and would like to finally put the idea to bed, one way or another, so I can get on with it or let it go!
Some background: I make a relatively low volume of high end hunting and kitchen knives. Right now the knives are made from A2 tool steel, but I will likely be moving to a stainless steel early next year. In either case the parts will be hardened to around 63HRC and all machining operations will be done on them in the fully hardened state.
Currently I machine the knives using a specialized set of fixtures:
Which work fairly well, but having to make fixtures like this for each knife shape that I want to make really robs me of my flexibility. It is also difficult to control chatter during the machining of the final blade bevel (the angled part behind the edge) because it means that I am clamping against a very thin blade, only 0.016" thick for my hunting knives and likely as little as 0.008" for my upcoming kitchen knives. Tolerance stack-up is also an issue across so many operations, and the fixtures do not allow me to reach all the surfaces that I would ideally like to be able to reach.
My goals for my process:
- Quality
- Consistency
- Flexibility
- Stable unattended operation
I make relatively few knives so speed is not of utmost importance to me. If the EDM operation took 2 hours or less then that would be completely acceptable. Faster is better to some extent because it would make the process more flexible, but speed is not a primary goal. For reference I only make about 30 knives per month.
The concept:
Basically I would like to buy steel stock that is oversized in all directions, harden it, then hard-mill the knife blade into the stock, but not actually cut it out. This would give me the flexibility to fully machine both sides of the blade without needing to make specialized fixtures for each model, and would give me more flexibility on the kind of steel stock I'm buying. Right now because I am not able to machine every surface (because fixtures are in the way) I have to buy precision ground stock with tight tolerances and tight surface finishes which drives up price. If I can machine all surfaces myself then I can buy hot-rolled descaled or cold-rolled stock and simply produce all final surfaces myself.
The output from the hard-milling operations would look something like this:
The two 3/8" holes at either end of the stock would serve as locating holes for the 2nd machining op and for the wire EDM op... I would then like to skim cut the inside of the pin holes in the handle to get final size and location, then cut out the profile of the knife with a single pass on the EDM. In the following screenshot the red lines indicate where I'd be cutting:
This would allow me to hold much tighter tolerances between the pin hole locations and the outline of the handle area. This is important because the fit between the metal parts of the handle and the G10 composite handles scales must be fairly tight because that area ends up directly touching the users fingertips, and any mismatch in dimensions or location above about 0.001" is fairly easily felt. Right now tolerance stack-up during the multiple machining operations makes this kind of a tricky target to hit and I would like to make it easier to get a better final result.
The edges where I'd be cutting with the EDM will generally be bead-blasted or sand-blasted so the matte finish from the EDM is not an issue at all.
The total length of the cut in the example above is 20.53" with most of the stock being 0.156" thick, though there are some sections that are thinner, namely along the cutting edge where the material is only 0.016" thick.
The advantages of wire as I see them for this process:
- More flexibility in design, no need to make specialized fixtures for every design change
- More flexibility with raw stock dimensions and tolerances
- Potential for more easily achieving tighter tolerances
- No burrs, which would reduce hand finishing and re-work from missed burrs
Disadvantages as I see them:
- Initial cost of machine if bought new
- Difficulty with parts availability and cost if EDM bought used
- Space taken up by another machine
- Cost of consumables
I'm curious what you guys think. Do you have any estimates for the time that this cut would take, and what the consumables cost would be? Is it utterly stupid to consider EDM for this process, or is it a process change that would pay off?
If wire EDM is not an option then honestly my other options for improvement are pretty limited. Making a fixture that would give the same level of access to all the surfaces that need machining is pretty much impossible. I could cut out the parts and leave tabs but then I'd be looking at follow-up machining or hand finishing operations which would make it harder again to hit the tighter tolerances that I want.
Any and all feedback appreciated!
Marcus: sorry for revisiting this, I know we spoke about this a while ago but I wanted to take the time to fully flesh out the idea and then finally put it to bed one way or the other!
-Aaron
I have been considering wire EDM for part of my production process for a few years, and would like to finally put the idea to bed, one way or another, so I can get on with it or let it go!
Some background: I make a relatively low volume of high end hunting and kitchen knives. Right now the knives are made from A2 tool steel, but I will likely be moving to a stainless steel early next year. In either case the parts will be hardened to around 63HRC and all machining operations will be done on them in the fully hardened state.
Currently I machine the knives using a specialized set of fixtures:
Which work fairly well, but having to make fixtures like this for each knife shape that I want to make really robs me of my flexibility. It is also difficult to control chatter during the machining of the final blade bevel (the angled part behind the edge) because it means that I am clamping against a very thin blade, only 0.016" thick for my hunting knives and likely as little as 0.008" for my upcoming kitchen knives. Tolerance stack-up is also an issue across so many operations, and the fixtures do not allow me to reach all the surfaces that I would ideally like to be able to reach.
My goals for my process:
- Quality
- Consistency
- Flexibility
- Stable unattended operation
I make relatively few knives so speed is not of utmost importance to me. If the EDM operation took 2 hours or less then that would be completely acceptable. Faster is better to some extent because it would make the process more flexible, but speed is not a primary goal. For reference I only make about 30 knives per month.
The concept:
Basically I would like to buy steel stock that is oversized in all directions, harden it, then hard-mill the knife blade into the stock, but not actually cut it out. This would give me the flexibility to fully machine both sides of the blade without needing to make specialized fixtures for each model, and would give me more flexibility on the kind of steel stock I'm buying. Right now because I am not able to machine every surface (because fixtures are in the way) I have to buy precision ground stock with tight tolerances and tight surface finishes which drives up price. If I can machine all surfaces myself then I can buy hot-rolled descaled or cold-rolled stock and simply produce all final surfaces myself.
The output from the hard-milling operations would look something like this:
The two 3/8" holes at either end of the stock would serve as locating holes for the 2nd machining op and for the wire EDM op... I would then like to skim cut the inside of the pin holes in the handle to get final size and location, then cut out the profile of the knife with a single pass on the EDM. In the following screenshot the red lines indicate where I'd be cutting:
This would allow me to hold much tighter tolerances between the pin hole locations and the outline of the handle area. This is important because the fit between the metal parts of the handle and the G10 composite handles scales must be fairly tight because that area ends up directly touching the users fingertips, and any mismatch in dimensions or location above about 0.001" is fairly easily felt. Right now tolerance stack-up during the multiple machining operations makes this kind of a tricky target to hit and I would like to make it easier to get a better final result.
The edges where I'd be cutting with the EDM will generally be bead-blasted or sand-blasted so the matte finish from the EDM is not an issue at all.
The total length of the cut in the example above is 20.53" with most of the stock being 0.156" thick, though there are some sections that are thinner, namely along the cutting edge where the material is only 0.016" thick.
The advantages of wire as I see them for this process:
- More flexibility in design, no need to make specialized fixtures for every design change
- More flexibility with raw stock dimensions and tolerances
- Potential for more easily achieving tighter tolerances
- No burrs, which would reduce hand finishing and re-work from missed burrs
Disadvantages as I see them:
- Initial cost of machine if bought new
- Difficulty with parts availability and cost if EDM bought used
- Space taken up by another machine
- Cost of consumables
I'm curious what you guys think. Do you have any estimates for the time that this cut would take, and what the consumables cost would be? Is it utterly stupid to consider EDM for this process, or is it a process change that would pay off?
If wire EDM is not an option then honestly my other options for improvement are pretty limited. Making a fixture that would give the same level of access to all the surfaces that need machining is pretty much impossible. I could cut out the parts and leave tabs but then I'd be looking at follow-up machining or hand finishing operations which would make it harder again to hit the tighter tolerances that I want.
Any and all feedback appreciated!
Marcus: sorry for revisiting this, I know we spoke about this a while ago but I wanted to take the time to fully flesh out the idea and then finally put it to bed one way or the other!
-Aaron