Cutting spinner slots

[Bob Reeves]

Just ordered two 2 inch spinners from Tru-Turn with special cut slots for a reverse pitch JFX prop. By the time I was done with the order I had spent over a $100.00 for two spinners. I can buy Brodak 2 inch spinners without cutouts for something less than $25.00 each but I have never had real good results trying to cut prop slots by hand.

I have a lathe and a mill and wondering if anyone has came up with jig or method to accurately cut prop slots using a mill? Am sure it can be done and I'm going to try it, just didn't want to reinvent the wheel if someone has already came up with a good way to get there.

[Chuck Feldman]

Bob,

You need to get a Dremel stylist tool. Lay it out and then cut them.

[Peter Nevai]

Ok so suppose you already have a dremel tool. What bit do you use? The abrasive wheels don't handle aluminum very well the grinding bits load up with aluminum and become useless after a couple of passes. The rest of the bits are for wood or plastic not aluminum.

Next question is how do you make sure that the cuts are exactly 180 degrees or 120 degrees apart and of equal span?

Yes you can stick the spinner on the prop and mark the rough locations of the blade notches. I don't think that is what Bob is looking to do. We are talking about contoured slots that follow the shape and ptich of the prop as it exits the spinner.

[Tim Wescott]

Here's my thought:

Turn up a sacrificial spinner back with a generous spigot that you can chuck up in your rotary table or clamp to a V block.  Bolt the spinner to it.  Now set the whole mess up in your milling machine at the correct angle such that a straight cut on the milling machine gives you a nice pretty slot.  Whack away.  Take apart, and clean up the cuts.

If you don't trust the spinner bolts to hold things together during the cut, make the sacrificial spinner back with a flange, and make a collar that fits the outside of the spinner just to the front of where you want your slots to end.  Bolt that onto your spinner back flange, and proceed with step "B" above.

You'll spend a lot of time making your fixtures, but once you're done you'll be able to whack out nicely controlled prop slots all day.

Or, you can just do it with a Dremel tool or a file.

[Tim Wescott]

Ok so suppose you already have a dremel tool. What bit do you use? The abrasive wheels don't handle aluminum very well the grinding bits load up with aluminum and become useless after a couple of passes. The rest of the bits are for wood or plastic not aluminum.

Most wood cutting burrs should work on aluminum.  If they don't, then you can probably get ones from McMaster-Carr.

Next question is how do you make sure that the cuts are exactly 180 degrees or 120 degrees apart and of equal span?

You mark them out very carefully, and you start by cutting them significantly undersized.  If you're smart, you make a gauge out of a bit of plywood that has 1/8" square "prop blades", and use that to make sure that your initial cuts are centered, then you work up from there.

Yes you can stick the spinner on the prop and mark the rough locations of the blade notches. I don't think that is what Bob is looking to do. We are talking about contoured slots that follow the shape and ptich of the prop as it exits the spinner.

I don't know -- Bob certainly didn't say so.  If he just wants straight cuts then this is an easy thing to do either by hand or on a manual mill.  If he wants contoured cuts then he darn near needs an NC mill with an NC rotary table; if he has those then he shouldn't need to be asking questions about fixturing!

If he does want a one-off, nicely contoured set of slots (as opposed to straight), then he's going to get there quicker with hand tools than with a machine anyway, even if his machine is NC.  Just cut the slots very tight to the prop to start with, and take care of any side to side differences as he puts clearance around the slots.

[Bob Reeves]

I can tell you right off the bat the Dremel is out, some people have the talent to do this stuff freehand, I do not so it doesn't matter what anyone says I will not do it with a dremel tool.

I do like the idea of being able to "whack out nicely controlled prop slots all day" and don't mind making the fixtures and buying the tools to be able to do exactly that. I do have a rotary table which will help insure the slots are in the proper location and Tim has given me a few ideas. I may never buy a slotted spinner again 

[Tim Wescott]

I'm with you on the Dremel tool front, Bob.  I didn't mention it, but whenever I try to cut something with one of those rotary burrs, I always end up getting things almost done, then losing control of the cutter and either making a notch in an otherwise straight cut, or running the cutter over some polished surface and ruining it.

I use hand files for things like that (which used to drive my dad up the wall when I worked on tooling for his shop -- he'd just use power tools for that and get them perfect every time; he could never understand my lack of sympathy with air-powered die grinders).

[Bill Little]

Hi Bob,

I hear you on the spinner slots "done by hand".  

But, I have found that making a template of the slot that can be tack glued to the spinner cone for marking out the slot to be invaluable.  I have a 1/8" bit that works very well for this and then use jewelers files to finish it off.

Not having a lathe or milling machine, I can only do things "by hand".

Big Bear

[Peter Nevai]

I'm with Bill, If it can't be done by hand I can't do it. I'll have to find a cutting burr that will fiit a dremel that cuts aluminum. Now if we can only stop that God Awful screetching noise associated with cutting aluminum with a cutter that would be excellent.

Abrasive wheels just can't accomplish this even though they remove material much more precisely.

Below is a link to McMasters and Carr Deremel compatible cutting bits.

http://www.mcmaster.com/#dremel-compatible-carbide-burs/=dtyufe

Alternative?

http://www.mcmaster.com/#dremel-compatible-sanding-bands/=dtz39l

[Dave Hull]

If I had a mill, I'd use it. But what I have, is a Dremel and files, and layout tools--so that is what I use. A few thoughts:

1. Using a straight flute carbide cutter in the Dremel and working in from the back edge works fine. They last a long time on aluminum.
2. If you trust your layout work you can drill a series of holes first, reducing the amount of Dremel work considerably. You can also use a small held-held saw to join the holes and finish the roughout. (Think of a short piece of hacksaw blade with a wood grip.)
3. Paper patterns work great as an aid for laying out slots. If you use engineering graph paper it is even easier. (Onion-skin, fine grid)
4. If you are machining away and don't like how the part is ringing--add support clamps or damping. Clay works well for damping.
5. Don't try to handhold the part and the tool. That never works well, except for whittling sticks. And guys cut themselves all the time whittling sticks!
6. For fixturing, you can bolt the spinner to a machinist's knee (spinner tip to the knee) and then rotate and tip the knee on the mill bed. Fill with clay. Use undersized cutter so you are only cutting on one side at a time to reduce loads.
7. Don't fall into the trap of wanting a perfect fit of the blade to the spinner as I have. First, you will need extra clearance to insert the prop into the minimum contoured slot you just made. The more thickness in the blade root, the more gap will be left behind as it seats. On full-sized planes they screw on an additional "filler" piece between the back of the prop and the spinner backplate. Also, the "perfect" slot will look less perfect when you want to try another prop and it won't fit. Been there, too.
8. What is harder to do is slot, or open up the slots, on a plastic spinner. Just doesn't seem amenable to as many methods as aluminum.
9. Check balance when done, including backplate and bolt/nuts.

Dave

[Douglas Ames]

Bob, if it was me I'd use my 90 deg. pneu. die grinder (Hi-speed) and a single cut rotary file, notching it out first with a cutting disc. Double cut rotary files just load up with aluminum too much. I understand you wanting precision. If I had machine tools and time I'd make a fixture

Thing is be sure to cut the slot profile to fit ALL your props you intend to run. Different blade profiles and all that.

[david beazley]

Bob, if you decide to make a fixture, please post some pix.  I have a Sherline mill and lathe and would like to try cutting my own slots too.

[bob branch]

I have found a cutter for the dremel that does aluminum pretty well and is easy to control. It is a rotozip zip bit ZBSC5 1/8 in Sabercut Zip Bit. Don't know how many years ago I got this pack of 5 but I got them at Sears and the sticker says $8.99. I think I have seen them at Lowes or Home Depot as well. They use the 1/8 inch collet in the dremel. It is a long cutter, about 3 inches and the cutting surface is pretty aggressive. I use it for probably 90% of my dremel work. It works well in Aluminum, wood, acoustical tile and fiberglass. You could also check it out on rotozip.com. Metal cut is pretty good and you can clean it up with a file or paper. In thin fiberglass its not quite so clean, but I do most of my cowl cutting with it and then use a small sanding drum to clean up.  I've been cutting spinners with it for yours. They do not load up very quickly and last a pretty long time. Don't require full speed from the dremel to do the job either. Always work with a finger brace, but it does not spin off like a round ball cutter will. I'm sure I have but I don't remember ever messing up a spinner with it.

bob branch

[Lee Thiel]

A bar of soap used on your rotary files will help prevent clogging.  Ya, I know Bob, your not going to use one.  
Lee  TGD

[bill bischoff]

I have gotten my best results using 1/4" drum sander bits with the Dremel. If this is too big a radius, I will do the final detail work with a 1/8" round jeweler's file.

[Bob Reeves]

N.D.D.

[Allan Perret]

Adding the right angle drive accessory to your Dremel gives you much more control.  Only about $15, try it you will like it.

[Terry Bernard]

Before you cut your hands with rotary bits, ruin your spinner or end up in the emergency ward, try the following. Make a narrow paper strip tape and mark the exact diameter of the spinner. Now divide the strip into two or three sections (two blade or three blade). Mark a dot at each cut out. Cut a blade from a broken prop of the same size you are going to use and use it to make a blade cut out template. Use the template to mark the blade shape on the spinner. Drill a small hole in the spinner at the leading edge point. Using a simple coping saw with a metal cutting blade cut out the shape of the blade taking the line. Refine/enlarge with files.   

Alternatively, paying the manufacturer to cut them out makes a lot of sense.

Terry.

[Bob Reeves]

Bumping this thread back to the front so it will be easier to find when I post the photo in a day or two. Lee Thiel brought over a chunk of 3 1/4" round aluminum. I cut a piece off about 3 inches long. First I clamped it to my mill and trued up the saw cut ends making sure they were 90 deg to the sides. installed the reverse chuck jaws on my lathe so it would hold the 3 1/4 " piece of aluminum and center drilled the free end so I could use the tail stock to help support the work piece. Then I turned all but about 1/2 inch of the whole thing down to almost two inches.

More and photo to follow.....

[Bob Reeves]

Almost ready to cut my first spinner..

After turning the the 3 1/4 stock down, I cut slots in the flange to mount it on the rotary table. Made an aluminum pin that fit the hole in the center of the rotary table and a 1/2 inch hole drilled in the bottom of the jig. this insures the jig is centered on the table when it's clamped down.

On the spinner end I drilled and taped a 1/4 28 hole in the center and use a 1/4 28 stud with the stock spinner parts to hold the spinner. Also cut a slot on the end so the little lip on the spinner that is normally captured by the back plate just fits. This insures the spinner is centered when it is attached to the jig.

[Steve Helmick]

I read in SN or on one of the stunt sites to use one of those contour copier thingy's...basically a bunch of pins clamped in the middle...to get a copy of the prop root cross section. I think the intended use is for complex shaped cove moldings and chair rails. Fairly cheap at any hardware store, but I'd bet you couldn't find one that's "hecho en EUA" if your life depended on it.  Steve

[Dick Pacini]

They are called a Profile Gauge and most hardware stores carry them.