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10-19-2012, 06:17 PM #1
Casting Epoxy and Tooling Recommendations
I'm a custom knifemaker and I want to reduce my hand fitting time and improve the fit where the knife handle meets the S-Guard. Currently, I make the guard, rough out the wood and inlet it using inletting black and tapping with a hammer, like a gunsmith does. Here's the picture - it's where the wood meets the metal guard:
In order to improve the fitup, I plan on using casting epoxy up against the metal guard and using the hardened epoxy as a template to machine the mating material with a drill press. I plan on running the tooling shank against the template. My questions are:
1)What epoxy system do you all recommend that will take the heat of the turning shank without collapsing? If there are none, should I use a high speed cutter with a bearing pilot?
2)Another knifemaker recommended a diamond type tool to sand the piece for a tight fit, but he never got back to me on either question. I imagine he was describing tooling like an end-mill but with small diamonds impregnated? Is there such a thing?
Thanks in advance,
10-19-2012, 08:41 PM #2
Personally, if I were doing this I would use software and CNC machining to make the parts. That could mean designing the guard with 3d modeling software, or making it by hand and using a 3d scanner to import the 3d part file. Then design the mating part(s) and use the software to generate toolpaths and let a computer guide the cutter. But that's just me (and many others here.)
By the way, the bearings in a drill press spindle are not designed to accommodate significant radial loads like milling would produce, and should therefore not be used for such. They're designed for the axial loads of drilling. You may be able to get away with "milling" wood for awhile, but something to keep in mind. Don't be surprised if your drill chuck with cutter () falls right out of the spindle or off its arbor in the middle of a cut...
To answer the questions you asked:
1. Depends on how fast you run the cutter, but probably better to use one with a pilot bearing.
2. Yes, they make diamond impregnated grinding bits, but that doesn't seem like the right choice for wood. Those are designed for hard materials. You need something with flutes to evacuate the wood shavings.
BTW, by responding I'm not in any way advocating the use of a drill press to do milling work.
10-19-2012, 09:34 PM #3
A casting epoxy would set up fast, I have heard people having good luck with Alumilite Alumilite - Products - Casting Resins, you could use a robo sander to follow the pattern *ROBO-SANDER FLUSH TRIM SANDER 3PK | Klingspor's Woodworking Shop good luck
10-19-2012, 09:48 PM #4
You may have given all the necessary info, but I am a little slow on grasping whether it is the metal or the wood part you want to machine.
I do a lot of this for various stuff so have a few ideas depending on which it is.
If it is the metal, I don't think free-handing it with a template against a spindle is going to be convenient unless all is mounted on a massive sliding (air?)table. My approach would be to make the template out of metal. probably hardened steel. It is a simple shape. If the intention is to freehand the form, I would then make the bearing to fit the table, like a pin router, concentric with but not attached to the cutter.
I make long run templates for cutting wood part out of linen phenolic. It may even be best for metal, too, unless you use hardened steel. I have not had good luck with epoxy cast templates partly because after adding the entry and exit ramps and accounting for the distortion to accommodate the bearing vs cutter size, it is easier to just lay-out and make one in phenolic. But if you prefer casting, it might make a good intermediate to use to cut the working template in another material.
If you don't want to go cnc, a Thomson table is the "old school" method of doing this work. It will mount to a mill or DP or even pin router if the work material is plastic or aluminum.
Even more common was a pantograph engraver/miller.
This is a 3D machine, but a 2D will work for what you want to do.
The Thomson table is 1:1 direct copy of a template
Depending on model, most 2D pantographs will do from 1:1 up to 8 or even 12:1 The advantage is the mechanical leverage and detail possible with the larger reductions. Wood, cardstock, plastic or plaster templates were common in the large reductions, even for cutting metal with small cutters.
15 -10 years ago there was an absolute flood of this type equipment on the market. Much has now been scrapped or soaked up. But I still occasionally see 2D pantographs for ~$200 or so. For some reason, Thomson tables are much scarcer. Probably few knew what they were, so it was easy to say "clean that area out and throw it in the dumpster". Plus being made out of aluminum, the beer & drug money was high (no pun intended) for that type item.
PS, I re-read your post a couple more times and it seems you only need to touch up the wood. In that case, I would use a pin router, or pin router type set up, so the pin is on the table. It may or may not rotate as the work (template) is pressed against it. On my Onsrud, the table pin is a light press fit in bearings (so the pin size can be easily swapped) and it does rotate from work pressure, but that is not essential. I have not done so, but can easily imagine setting the spindle to low speed, and using a small sanding spindle in the collet with factory sleeves as the "cutter" for touch up or fitting type work.
10-31-2012, 12:48 AM #5
I used to make Deckel models with a hard surface coat. I think it had a carbide fill. Maybe something like that would work .
Check Freeman Supply.
10-31-2012, 08:46 AM #6
I've used a sanding spindle as Stephen describes above in my drill press to shape banjo pegheads. You need to make a base plate with a hole for the guide pin which will clamp or bolt to the table. The pin needs to be the exact diameter of the sanding sleeve, and perfectly co-axial with the spindle. If you sand with more than one grit, you'll need a pin for each, as the OD will be different.
The best thing about sanding rather than cutting is there will be no tear out, no grabbing, and radial load on the drill press spindle can be controlled by how hard you push on it. I made the sanding spindle with a small bearing at the end, which fit into a bored hole in the guide pin to support it.
But even with all that, i doubt you'll get an accurate enuf contour to get a perfect fit. I think you'll still need to do hand fitting to make the joint perfect.
10-31-2012, 11:23 AM #7
per B sco; I've also used the Freeman's for 3D models, but mine did not need the carbide filler due to relatively small batches of parts. I just use the standard blue (glass filled) "reprothane". For a thin 2D model, I might try graphite filled WEST epoxy with perhaps some cotton fibers thrown in as well, limitations as noted in my previous post.
Any updates or comments from the OP?
11-01-2012, 07:47 AM #8
Epolite is an iron filled epoxy available from Kindt Collins (now owned by Freeman) that was often used for Deckel models. There is aluminum filled epoxy available as well. However for the one off uses that you are thinking of as long as you use a pilot bearing on the router bit Bondo would work just fine, I have used Bondo to make templates used for a router bit. Epoxy involves waiting overnight before you can use the template Bondo could be used in 20-30 minutes. The last time I bought iron filled Epolite a 5 gallon unit was about $800 I don't think it is available in smaller units. I would use a router table or hand held router with the work well fastened down rather than a drill press. A spinning router bit in a chuck can get really exciting when it drops out of the morse taper. As well the drill press will not turn fast enough.
This will get you very close but you are still going to have to do a little final fitting to get the kind of perfect fit you show in your picture.
Just re read above posts and I agree the piloted sanding drum might be better and definitely safer.