Author Topic: Machining question (Read 1713 times)

handirifle · « **on:** August 31, 2012, 08:19:37 PM »

This is not a gunsmithing question, but after an unsuccessful web search, I am hoping someone here can help me, in what I have in mind. This is an archery related machining question.

What I have in mind, was something I read about on the web, so here goes. I want to take a conical shaped screw in typ of field arrow head, you know the kind that looks like a bullet?

Picture the head, standing with the point up, and the threaded end down. It would be the bottom point in this picture, or one like it.

This is a picture posted at Tradrag.com, and it is where I got the idea. in this pic he uses a hollow, glue on, field point, whereas I want to start with a solid screw in type. Mainly for more weight and that I am using carbon arrows.

here is the link to see the entire thread... http://www.tradrag.com/forum/viewtopic.php?f=35&t=585

Note also, that his "jig" is a two piece block that holds the head for cutting. What I would like to do is mount a small metal cutting blade on a shaft turned by the chuck on my lathe, and make some sort of jig that would mount into the tool holder, and be able to guide it in with the carriage.

My question, is this, is there some way that I can rig this up to insure that I cut exact center (or as exact as me and the lathe can be) on a repeatable basis? the jig in the picture seems like it worked, but looking at another picture in the thread, it looks off center. He mentions he had accuracy problems, which leads me to believe there might be concentricity problems.

Any suggestions will be appreciated. Also if this isn't the best place to ask this, but you know of a better site, I would be happy to post there.

Thanks, and let me know if you need more input.

BW56 · « **Reply #1 on:** September 01, 2012, 07:15:36 PM »

Seems backwards to me if i'm reading it right. I'd replace the lathe chuck with a collet set up. You can use a custom collet bored to the exact I.D. size with a stop screwed in the back of it. That would solve the concentric issues. The one i used had a hand wheel to tighten the collet. Some had an adjustable lever to open and close the collet. Don't work there anymore and don't know cost. I'd try looking at Enco.com to start with.

handirifle · « **Reply #2 on:** September 01, 2012, 08:34:04 PM »

I see what you're saying, except I do not understand how I could cut a slice in the workpiece while it is spinning in the collet. If I wanted to drill a hole in the workpiece, yes, but not a cross slice.

I envisioned being able to put a 2" metal cutting blade on a shaft mounted in the chuck. This blade would be perpendicular to the chuck, kinda like a dremmel tool with a cutoff blade. That way, I could mount the workpiece in the carriage and control the depth of cut.

Maybe I am thinking this all backwards, but I thought that way, if i could align the workpiece centered on the spinning blade, I could turn the carriage and cut the slot.

With the way you describe, I cannot see where I would mount the saw blade. correct me if I am missing your point, please. I am just throwing out what is in my head, and I am NOT a machinist at all.

handirifle · « **Reply #3 on:** September 01, 2012, 08:58:49 PM »

Thinking this over a bit, I thought of a couple things. One, imagine I am trying to cut a vertical slice through a cylinder, standing on one end. That is the type of cut I want to make.

The other thing i thought of , was, that I could get the exact diameter of the piece, then run the piece up against the saw blade, and then go past it, exactly half the diameter of the piece, and that SHOULD be center.

Keith L · « **Reply #4 on:** September 02, 2012, 06:32:51 AM »

I don't know why you would use a lathe to cut a slot lengthwise. I would use a mill and a fixture somewhat like the one in your picture.

handirifle · « **Reply #5 on:** September 02, 2012, 06:50:12 AM »

Because I don't own a mill, and I just own a small mini-lathe. That's why I was trying to come up with a way to use the lathe to control the cutting. I do not have access to anyone that does own a mill, unfortunately.

gunnut69 · « **Reply #6 on:** September 02, 2012, 10:37:52 AM »

Chuck the die grinder in a bracket held in the lathes cross feed..or milling attachment, hold the point in a collet..? An angle iron would hold the work piece and the center would be the bottom of the 'v'. Attach to the cross slide and turn the tool with the chuck... Theres a lot of ways to skin this..

handirifle · « **Reply #7 on:** September 02, 2012, 04:41:17 PM »

I apologize for being thick, but I cannot make a mental picture of this.

handirifle · « **Reply #8 on:** September 02, 2012, 07:57:42 PM »

OK I threw together some pieces, to show in picture form what I want to do.

Hope this explains it better. The blade that is turned by the chuck, will cut into the arrow point, and the tip of that point is what I wanted to center on the blade. The reason is to keep it concentric to permit the best possible arrow flight.

Eventually I will fabricate my own, longer, more tapered points for this project, but am using this one as an example. I have already made longer heavier points (some over 300gr) but I wanted to use this one as a learning/setup tool.

This first one shows the point aligned (somewhat) with the blade. This is what I want to achieve, but am hoping to learn of a way better than "eyeballing".

Numbers 2 and three, just show the same thing from different angles.

Thanks so much for the feedback so far. Much appreciated. Currently, the shank of the tip is held down by the tool holder screw, with a cutting tool under it for height adjustment. I will make a threaded block to thread the tip into, that will hold it securely, for my final work.

PS. yes I do know the blade is upside down

, this was for illustration only.

gunnut69 · « **Reply #9 on:** September 03, 2012, 04:36:16 AM »

A 90 degree groove in the holder will easily be aligned with the blade and round objects will self center.. The groove's 2 walls should each be 45 degrees from the verticle to form an included angle of 90 degrees, i.e. angle iron..

handirifle · « **Reply #10 on:** September 03, 2012, 08:34:42 AM »

So for a visual, the point, or workpiece, of round steel, instead of sticking out there like in the pics, it should be cradled in the "V", with each side of the V 45 deg from the blade?

That sounds reasonable, and I see how it would self center. Question, how would you measure the 45 deg angle on such a small scale? I have wood tools to do that with, but nothing that will even come close to fitting in there? Should I just measure them equal distant from the blade, and THEN cut the groove in the angle?

I have some aluminum angle that might work real well for this. How would you suggest mounting the angle in the tool holder. Mine uses a series of set screws to clamp it to the lower half of the holder?

I really appreciate the feedback, I realize this is basic stuff for you guys, but it's an everyday learning experience for me.

Ranger99 · « **Reply #11 on:** September 03, 2012, 08:45:40 AM »

excuse my butt in. . . .

what are you trying to make?
are you trying to make broadheads?

handirifle · « **Reply #12 on:** September 03, 2012, 09:07:53 AM »

The more the merrier! Yes I am. Thinking saw blade cut into proper shape and pinned then soldered onto the screw in shank. That is what I am trying to cut the slot into. The point in the pic is for reference only. I will make shanks about 1 1/4" long.

Ranger99 · « **Reply #13 on:** September 03, 2012, 11:37:43 AM »

ok. . . .
i kinda thought so.
seems like a lot of trouble, but then
again, some of the store-bought heads
i've used didn't impress me much.
when you handcraft something, all the
small details get took care of more so
than an assembly line.

good luck with 'em
post a pic with whatever you take

handirifle · « **Reply #14 on:** September 03, 2012, 01:56:21 PM »

Yea and this year am switching to the heavy, single bevel design, and for the low cost ones, they are over $60 shipped for only 6 heads. They go up from there. I I can can some money and improve my work at the same time, its a win-win.

handirifle · « **Reply #15 on:** September 04, 2012, 06:31:22 PM »

Well, my idea, as conceived, isn't going to work. The blade I am using is apparently too thin, as it starts to curve in the cutting process. That is not acceptable. Unless I can come up with a blade that is thicker and more stable, yet affordable I may have to get them the old fashioned way, buy them.

I will keep looking for a better blade in the meantime.

Ranger99 · « **Reply #16 on:** September 04, 2012, 06:43:23 PM »

what about sawzall-type bi-metal blades?
(or is that what you're using?)

Ranger99 · « **Reply #17 on:** September 04, 2012, 06:44:24 PM »

or even discarded circular saw blades?

handirifle · « **Reply #18 on:** September 04, 2012, 07:07:11 PM »

The blade in question, is the little 2" circular blade in the picture. It is the one actually doing the cutting. This whole idea was to cut the shank or shaft portion of the broadhead, so the broadhead blade could be inserted into it and pinned and soldered in place.

I plan on starting with circular saw blades as the first generation of broadhead blade, if I ever get that far with this idea. There's a LOT of areas this project can go awry. That was just one of them. The blade was also too thin, because it didn't cut a wide enough kerf to insert the broadhead blade into anyway, so back to square one.

not the first time this has happened to one of my "projects", but no biggie, I just keep learning new things along the way.

handirifle · « **Reply #19 on:** September 04, 2012, 07:11:59 PM »

Actually, after thinking back, I cut the field point mounted in the tool holder, as you see in the pic. It MIGHT

(meaning most likely it was) have been a little off square as well. Maybe I will try to make a jig that will align square and try it again. I have to say, it cut the point quite easily. Not bad for a little Harbor Freight blade.

Even if it does cut straight, it will be a thin kerf, so I will have to solve that issue as well.

Ranger99 · « **Reply #20 on:** September 04, 2012, 07:23:39 PM »

well. . . .
you have more patience than i do.
i still have a few of those old-timey
magnus two blade heads i like, and
some of the old-timey thunderheads.
i've had my brief affair with mechanicals,
and kissed goodbye.
i hope i can still get some replacements
in the future without having to plunk down
a tenner apiece.
again, good luck with it

handirifle · « **Reply #21 on:** September 05, 2012, 02:35:12 PM »

Yea, the cost of broadheads, like everything else, has gone through the roof. Was pricing feathers, for fletching, and THEY are almost a dollar each. Unbelievable! Sure glad I am so much better off now than I was 4 years ago!

JustaShooter · « **Reply #22 on:** September 05, 2012, 03:54:08 PM »

You might try stacking two of the thinner blades together to make one thicker blade - it won't be twice as thick, it will just add the thickness of the metal to the kerf of the cut. It will stiffen things up too...

Just a Shooter

handirifle · « **Reply #23 on:** September 06, 2012, 06:17:53 AM »

Quote from: JustaShooter on September 05, 2012, 03:54:08 PM

You might try stacking two of the thinner blades together to make one thicker blade - it won't be twice as thick, it will just add the thickness of the metal to the kerf of the cut. It will stiffen things up too...

Just a Shooter

Good idea, will have to give that a shot. As I mentioned also, I need to make a holder that will allow me to insure the workpiece is truly perpendicular with the blades.

gunnut69 · « **Reply #24 on:** September 06, 2012, 02:16:04 PM »

Try clamping an angle iron section to the tool holder and the cylinder to the 'v'. Center using a straight steel scribe to point from the center of the 'v' to the blade center. A dial indicator can be used to find the center of both the blade and the clamp jig. Once indicated in the setup would geometrically replicate at each cylinder mounting..

handirifle · « **Reply #25 on:** September 07, 2012, 07:22:35 PM »

OK here's what I cannot get a picture of in my head about the whole angle iron idea. The V makes perfect sense, but do I clamp it with the V up, or clamp one side flat, like an L? If clamping it like a V, then how do I know it's not off to one side?

If I picture the V positioned perfectly, then the blade should line up with the center of the V quite easily, but I am not sure how to insure the V isn't leaning ever so slightly to one side.

Sorry for being so thick.

gunnut69 · « **Reply #26 on:** September 08, 2012, 07:42:07 PM »

A holder could be made by machining a square groove 45 from perpendicular.. The absolute verticality of the holder is not super relavent as long as the v groove is centered to the blades travel. Use a dial ndicator to center the blades and the 'v' holder..

handirifle · « **Reply #27 on:** September 09, 2012, 01:11:21 PM »

OK I get it now. I will have to see if there is enough room in my tool holder to fit all that in. It's just a little Harbor Freight 7x12 lathe.

Thanks for your patience.

Ranger99 · « **Reply #28 on:** September 19, 2012, 06:15:22 PM »

where did the project end up? $:-\$

handirifle · « **Reply #29 on:** September 19, 2012, 08:14:04 PM »

I am embarrassed to say that, like an idiot, I cracked the upper limb

. Rather PO'd at myself at the moment, so the real answer to your question, is that it is on hold. Thanks for asking though. I guess when I have the dealer REPLACE the limb, I will let him time it. Boy glad I saved money on that project?