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DICKEYBIRD
08-15-2010, 10:21 AM
I'm grinding a lathe form tool from a 3/8" stick of HSS and am having trouble getting my head around how to position it as I follow the profile shown. The tool will be plunged into a 9 mm hole in 6061 to form the ID of a venturi.

So far I've kept it parallel to the wheel as I roughed it but now need to properly shape the tighter radius of the quarter elliptic profile. (The template was drawn in CAD and glued to the blank with CYA glue.)

The table is clamped at 30 deg. The grind so far has been on the left side of the wheel which is spinning c/cw. I'm thinking I need to reverse the wheel rotation and approach it from the right side with the blank rotated about 45 deg c/cw, rotating the blank c/cw as I follow the profile to where it meets the edge, keeping the template line parallel to the face of the wheel as I rotate the blank. Does that make sense?:confused:

Edit: Oops, the picture fool.

http://i57.photobucket.com/albums/g227/DBAviation/NR60FormToolGrind.jpg

DICKEYBIRD
08-15-2010, 11:02 AM
:rolleyes:

TGTool
08-15-2010, 12:02 PM
Can you raise the rest so that the small radius is presented to the wheel somewhat above wheel center height? This means the wheel will be undercutting the tool and providing the clearance you're looking for below the cutting edge. There are formulas for determining how much height above center is an approximation of a specific clearance angle but you may be able to eyeball it satisfactorily. You'll have a straight clearance surface transitioning to a concave one but that shouldn't be a problem in use.

DICKEYBIRD
08-15-2010, 12:16 PM
Never thought o'that! But no, it's a standard HF Baldor clone and it's rest only pivots, won't raise lower. I'm now trying the method I posted above and it looks pretty close. I'm sure I'll have to blend in the final shape with a Dremel tool. It should work...but the proof'll be in the chip. Shiny & slick hopefully; not dusty & smeared.:)

Toolguy
08-15-2010, 01:31 PM
The method of grinding the contour you propose will work fine, but you'll have to grind a lot off the bottom to get it into a 9mm hole. 3/8 is about 10mm and you need the cutting edge to be at half of 9mm. Also, you will need additional back clearance along the skinny part due to the curvature of the hole below the cutting edge. That's a 2 part operation. Get the contour right, then grind until you get enough back clearance behind the cutting edge.

dp
08-15-2010, 01:33 PM
You can clamp a wedge shaped riser to the grinder table to get the angles you need. I've used hardwood for this because the smoke smells better than yellow pine :)

DICKEYBIRD
08-15-2010, 02:39 PM
It works! I had drawn the thing in CAD to get the angle and dimensions right to make sure it would go in the hole and had enough relief to keep it from dragging. After getting the basic shape pretty close, I smoothed it up with a Dremel with the little sanding drum and polished it up by hand with a diamond lap. It peeled off nice shiny ribbons of swarf and left a great finish. Hoo-yah!

http://i57.photobucket.com/albums/g227/DBAviation/NR60FormTool.jpg

http://i57.photobucket.com/albums/g227/DBAviation/NR60FormTool2.jpg

http://i57.photobucket.com/albums/g227/DBAviation/NR60FormToolCut.jpg

Toolguy
08-15-2010, 02:57 PM
Great Job!:)

Dr Stan
08-15-2010, 03:10 PM
Great job on the cutting tool. However, leave the gloves on the bench or in the tool box when using a grinder. Even the disposable gloves increase the chance of getting tangled up in the wheel and that's not a pretty sight.

DICKEYBIRD
08-15-2010, 04:12 PM
Thanks Doc, you are, of course, right. I forget sometimes.

Here's the finished product it came out real nice:

http://i57.photobucket.com/albums/g227/DBAviation/NR60Venturi.jpg

Goes here:

http://i57.photobucket.com/albums/g227/DBAviation/NR60.jpg

It's a custom venturi that goes on a .60 cu. in. high power Italian R/C model engine. The venturi goes in place of the R/C carburetor since the engine will be used in a control line model. The fellow that will fly it must have gorilla arms 'cuz this thing has some serious Italian (not Chinese;)) horsepower.

Dr Stan
08-15-2010, 06:35 PM
Thanks Doc, you are, of course, right. I forget sometimes.



Very nice work. BTW, I had to take a student for medical attention due to his leaving gloves on when using the grinder. Pulled his thumb between the wheel and the inside of the wheel guard. No fun, especially for him.

Oldbrock
08-15-2010, 07:11 PM
Great final result on the grind job, was going to suggest a dremel for finishing but you beat me to it. I concur with the glove danger. Don't even forget once, that is when you are digging your thumb from between the wheel and the rest. Repeat kudos on the finished tool. Peter

wendtmk
08-16-2010, 08:37 AM
http://i57.photobucket.com/albums/g227/DBAviation/NR60.jpg[/IMG]

It's a custom venturi that goes on a .60 cu. in. high power Italian R/C model engine. The venturi goes in place of the R/C carburetor since the engine will be used in a control line model. The fellow that will fly it must have gorilla arms 'cuz this thing has some serious Italian (not Chinese;)) horsepower.

DB,

Is that a Rossi? I used to muck around with the Rossi .40's which put out damn near as much power as most of the regular .60's. A Rossi .60 is definitely a brute to be reckoned with.

Mark

Mcgyver
08-16-2010, 08:47 AM
nice work DB, I was a little concerned with the DOC of the tool and how unsupported it was but that came out very well

Evan
08-16-2010, 09:29 AM
Great job. I make similar form tools from HSS and it's amazing how well they work even with very long unsupported shapes.

DICKEYBIRD
08-16-2010, 09:39 AM
DB, Is that a Rossi?Mark it's a NOVAROSSI which is a separate company. 2 brothers, 2 different brands of engines, both built with incredible precision and state of the art manufacturing. Check out the video at http://www.novarossi.it/eng/history/?brand=nova

Thanks Michael. I shared your doubts but my machining mentor showed me that it would work a few years ago on a similar project. Probably wouldn't work as well on harder metals but it does fine on 6061. I do have to keep the speed down, go easy on the feed rate and keep the lube flowing. There's definitely some flexing at the tip but a few slow passes near the end, lingering a bit when fully inserted until the fine chips stop does the trick.

I'm amazed at the wide, shiny chips that curl out of the hole with no sign of chatter when the the speed & feed are right. I took the compound off my little lathe yrs. ago and mounted the QCTP directly to the cross-slide. The extra rigidity really helps doing stuff like this.

I daydream about building a small CNC lathe to do these venturis but the appropriate good junk hasn't showed up yet.

DICKEYBIRD
08-16-2010, 09:48 AM
...and thanks to you as well Evan. :D

Evan
08-16-2010, 09:58 AM
For a job like that your form tool beats CNC easily. It would take a fairly long run time to make something like that with a CNC and it wouldn't look as pretty.

ldn
08-16-2010, 10:00 AM
That is a very nice looking doodad you made!

How did you know what kind of curve to use for the venturi? Is it just a "by eye" kind of thing?

RichardG
08-16-2010, 10:35 AM
Very nice will have to try that sometime.
Richard

DICKEYBIRD
08-16-2010, 11:13 AM
That is a very nice looking doodad you made!

How did you know what kind of curve to use for the venturi? Is it just a "by eye" kind of thing?Thanks Richard. This one has a quarter ellipse shape drawn in CAD. The pundits say a parabola is best but I had trouble trying to draw one in TurboCAD. I don't think the shape matters a lot to be honest. Some well known modelers just use a straight taper and they work fine. Go figure.

I do these for a buddy who's the importer so I try to make them look like I know what I'm doing.:D Ellipses are quick & easy in CAD. It took a while carving off all that HSS get a usable tool though....and cleaning up the A/O dust everywhere afterwards. Which reminds me, I need to make a containment curtain to go around my grinding station before the next big grinding session. Man, what a mess!

Evan
08-16-2010, 11:47 AM
The pundits say a parabola is best but I had trouble trying to draw one in TurboCAD

The circle is a special case of the ellipse. The ellipse and the parabola have a congruency where they share the same curve. To very closely approximate a parabola in any 2D cad program draw a circle and scale the Y axis by a very large amount. Then trim off one end of the semi major axis to use as a parabola. It may then be scaled however you wish.

DICKEYBIRD
08-16-2010, 01:05 PM
Hmmm, how 'bout that. I'll play around with that next time I need a parabola. One never knows when a parabola will save the day!:)

madman
10-21-2010, 01:07 PM
Brings back memories of U Control Goodyear racing. Three guys in centre of Lot with 3 planes powered by Rossi 2.5 cc (.15 ci0 engines running lOTS of Nitro, They were fast and it was fun having 3 planes in the air at a time. pit stops included 100 and 200 Lap Semi and Final Heats. Seems Kids dont do much anymore of anything?

DICKEYBIRD
10-21-2010, 01:27 PM
Me too on the memory lane trip madman. Ukie racing's some of the best fun I've ever had. I've raced r/c .40 Quickee 500's, .28 Quickees and unlimited r/c speed and I can't say it was as much fun as fun as 4 up mouse racing. That was more fun than I could stand. We did 50 lap heats and a 200 lap final on 35 ft. dacron lines with HOT Cox .049's. After about 5 laps the world turned into a queasy blur.

It was a lot more fun once we'd all puked up everything we'd eaten including the remnants of last Thanksgiving's dinner.:D Just think of all the good beer we could save by getting kids to spew their guts up doing some u/c racing instead of weekend-long keggers!