Enlarging Propeller Holes

[Serge_Krauss]

Guys, I could use some more expert advice. Jim Lee sent me a nice shaft extension prop nut which requires me to drill out my (approx) 1/4" APC prop holes to 5/16" diameter. I tried to drill out an old broken APC concentrically, and found that I could not center the enlarged hole accurately enough by just re-drilling with the larger diameter bit. So I ordered an very inexpensive step drill bit set from Amazon.

The good news was that it arrived in one day. Unfortunately, the diameters of the steps needed aren't all consistent and accurate. I need to start at .250" and finish concentrically at .3125" The three bits shown have these indicated OD's at the 1/4" and 5/16" markings, top to bottom in the photo.

                       1/4"                            5/16"

Top:            2.36" - .238"                   .297"-.298"
Middle:       .242" - .252"                    .299" - .313"
Bottom:      .244" - .252"                    .309 - .313
 
I think I can use the middle bit, but the one I'd planned on (top) rattles around in the hole at the 1/4" step so much that I don't think I can make a reasonably centered hole. The other's (bottom) steps are probably a bit short to be able to drill through from just one side.

So my questions are just whether these discrepancies are to be expected in cheap step drills, and whether I'm going about this simple task the right way. All advice is welcome! Thanks.

SK

[Dan McEntee]

    Serge;
  You need a Fox, or some other brand prop reamer. They are essentially step drill but with much longer steps. There are two kinds. One is standard US sizes that has four steps and goes from 1/4" to 3/8" I do believe. The metric unit has three steps and does 7, 8 and 10mm I think. Great Planes may have some thing similar, but I don't know of any others that are available. I have had the Fox units for years and is all I use. they are pretty accurate. If I need to step a prop hole down, I use Evergreen styrene plastic tubing that is 3/8" O.D., cut off a small piece, then glue it into the hole. Then I use the prop reamer to take it out to the size I need.
  Good luck and have fun,
   Dan McEntee

  PS to add: You may not want to use a drill to do this. The Fox reamers are a T handle affair. You may want to try your step drill in a T style tap handle and see ifi that gives you the control you desire.

[Larry Fruits]

Serge,
 By far the best way to enlarge the shaft hole in a propeller is to use a piloted counterbore. There are two types. Either fixed pilot, (integral), or removable, (interchangeable). They are available from McMaster Carr and are fairly reasonable when one considers the accuracy they provide.
 Just go to the McMaster Carr website https://www.mcmaster.com/#counterbores/=1amkwt7 and select "High Speed Steel Changeable-Pilot Counterbore", for the counterbore, or select "Steel Pilots for Changeable-Pilot Counterbores" for the pilots. Just make sure you match the shaft diameter on the pilot to the hole size in the counterbore. They come with different shaft and hole diameters. They must match. Sorry I couldn't get the direct link for each to work here. They can be used by hand, but for best results, use them in a drill press.

 I use the removable pilot type, as it gives me more flexibility than with the built in type.

 Also to reduce the shaft hole diameter, one can use brass tubing cut to length as bushings. The brass tubing is telescopic in sizes and are very accurate giving a nice fit without having to ream to size after installation in the prop.

 Dan's method will work, but I find the above to be more accurate and much easier to accomplish.

 Good luck;
   Larry   

[Tim Wescott]

And balance the prop, indexing off of the hole you're going to use to locate it to the engine, after you enlarge it.

[Dan McEntee]

The above two methods assume the hole is on center to begin with. A third way is to use a drill guide that seats on the front of the hub and centers on the relief in the hub. Of course you need a lathe to make one.

MM

     That would require the relief, if it has one, to be concentric also. APC has been known to make props with the holes off center, but not very often. If you check balance with a good balancer, you can detect the offset hole that way without any measuring. In the 50 some odd years I have been flying model airplanes, I think I have found one or two props that I can remember. APC stands behind their product in that respect an I would expect that any manufacturer would also.
   Type at you later,
   Dan McEntee

[Howard Rush]

The 1/4” hole in the front of APC props I’ve used has often been off center, thus not useful for indexing a larger hole. The 3/8” dent in the back of the props, however, is centered. After trying to relocate the 1/4” hole using epoxy and a fancy fixture clamped to a drill press, I ended up drilling the props from the back with a 3/8” bit and using a spacer when necessary. This was for hefty-hub combat props. I don’t remember if it works for the C-2 hub.

[Wayne J. Buran]

Guys, I could use some more expert advice. Jim Lee sent me a nice shaft extension prop nut which requires me to drill out my (approx) 1/4" APC prop holes to 5/16" diameter. I tried to drill out an old broken APC concentrically, and found that I could not center the enlarged hole accurately enough by just re-drilling with the larger diameter bit. So I ordered an very inexpensive step drill bit set from Amazon.

The good news was that it arrived in one day. Unfortunately, the diameters of the steps needed aren't all consistent and accurate. I need to start at .250" and finish concentrically at .3125" The three bits shown have these indicated OD's at the 1/4" and 5/16" markings, top to bottom in the photo.

                       1/4"                            5/16"

Top:            2.36" - .238"                   .297"-.298"
Middle:       .242" - .252"                    .299" - .313"
Bottom:      .244" - .252"                    .309 - .313
 
I think I can use the middle bit, but the one I'd planned on (top) rattles around in the hole at the 1/4" step so much that I don't think I can make a reasonably centered hole. The other's (bottom) steps are probably a bit short to be able to drill through from just one side.

So my questions are just whether these discrepancies are to be expected in cheap step drills, and whether I'm going about this simple task the right way. All advice is welcome! Thanks.

SK

Serge, you don't use drills to open up an already drilled hole ever. Reamer only preferably a "hand reamer" for the correct size which by the way has a long chamfer on it. That said the current hole should not be smaller than the small end of the chamfer. You may need two reamers if you want to do it correctly. You should not use a c'bore with a removable pilot because you can't properly secure the prop.
Wayne

[Larry Fruits]

 Well, a machine vice and a drill press work pretty good, and much better than trying to hold a prop by hand and using a hand reamer. Not trying to create an argument, just a fact.

 If you find the shaft hole to be off center in the prop, the counterbore can be use without the pilot to "re-center" the hole. A counterbore is flat on its end and cuts as it fed into the material being cut. Go slow and it will work fine. Of course this must be done in a drill press. End cutting end mills will work the same for re-centering. Don't use a drill, as it will tend to move and follow the original hole. Use a flat bottom, end cutting tool. And as Tim said, always rebalance. I assumed one would do that and left it out of my original post.

 Good luck;
   Larry

[Larry Fruits]

Deleted... duplicate post... sorry
 

[Fredvon4]

Is there any Lee machine type supplier who has made a drill guild that keys to the Proper/centered APC molding to center cut a proper hole?

I don't really care about an over sized hole as I  know how to sleeve it down... but reaming or drilling in the already /miss drilled offset hole is a waste of time

About 30% of my APC collection is worthless..... depending on how you look at it... they are cheap so what..... or ...there are too cheap to bother with sending back....

[Fred Underwood]

The 1/4” hole in the front of APC props I’ve used has often been off center, thus not useful for indexing a larger hole. The 3/8” dent in the back of the props, however, is centered. After trying to relocate the 1/4” hole using epoxy and a fancy fixture clamped to a drill press, I ended up drilling the props from the back with a 3/8” bit and using a spacer when necessary. This was for hefty-hub combat props. I don’t remember if it works for the C-2 hub.

APC noted that the through hole may, probably is, off center.  Only the back hole is centered. I have found the easiest way to balance and use APC's is to over drill the through hole so that it cant touch the shaft and then align the prop with supplied sleeves/adapter rings.  If you can't use a sleeve/ring, then I might not use APC.

[Howard Rush]

About 30% of my APC collection is worthless..... depending on how you look at it... they are cheap so what..... or ...there are too cheap to bother with sending back....

Give them to me. I’ll fix them and use them.

[Tim Wescott]

APC noted that the through hole may, probably is, off center.  Only the back hole is centered. I have found the easiest way to balance and use APC's is to over drill the through hole so that it cant touch the shaft and then align the prop with supplied sleeves.  If you can't use a sleeve, then I might not use APC.

I think they only recommend the sleeves for electrics.  I've always found the 1/4" holes to be accurate enough for me with the sizes I use for slime engines, but maybe I'm just not picky enough (I figure that if I put it in my balancer and the resulting pendulum has a period over six seconds then it's golden -- I have yet to shake a plane apart).

A drill bushing would be the bee's knees, but the off-the-shelf ones from McMaster don't seem suitable.

Serge -- call Jim Lee and present it to him as a challenge.  It should be easy enough to make one, and even harden it so that it'll last for a good long time.

[Air Ministry .]

Whacking the drill press through APC props for the ETAs resulted in trauma, depression & anxiety in the majority of cases for me .

Ever After ive periodically contemplated finding a Prop Reamer . 

I think youd need to clamp the prop down , AND be very cautious , to put a drill bit through them .

[Dave Harmon]

Guys, I could use some more expert advice. Jim Lee sent me a nice shaft extension prop nut which requires me to drill out my (approx) 1/4" APC prop holes to 5/16" diameter. I tried to drill out an old broken APC concentrically, and found that I could not center the enlarged hole accurately enough by just re-drilling with the larger diameter bit. So I ordered an very inexpensive step drill bit set from Amazon.

The good news was that it arrived in one day. Unfortunately, the diameters of the steps needed aren't all consistent and accurate. I need to start at .250" and finish concentrically at .3125" The three bits shown have these indicated OD's at the 1/4" and 5/16" markings, top to bottom in the photo.

                       1/4"                            5/16"

Top:            2.36" - .238"                   .297"-.298"
Middle:       .242" - .252"                    .299" - .313"
Bottom:      .244" - .252"                    .309 - .313
 
I think I can use the middle bit, but the one I'd planned on (top) rattles around in the hole at the 1/4" step so much that I don't think I can make a reasonably centered hole. The other's (bottom) steps are probably a bit short to be able to drill through from just one side.

So my questions are just whether these discrepancies are to be expected in cheap step drills, and whether I'm going about this simple task the right way. All advice is welcome! Thanks.

SK

Serge.....
I have done this a LOT....
Use a tapered reamer....never a step reamer or drill.
It is reamed from the rear of the hub....do not go all the way through....you only want the front of the hub to fit snug on the shaft so the prop will be on center.
The exact instructions are on the APC site and some size props come with a printed sheet showing how to properly ream these props.
Also...some sizes have inserts for different size shafts.

[Fred Underwood]

https://www.apcprop.com/technical-information/technical-support-advisories/

If I interpret correctly, the through hole is not reliable for center or balance, and the shaft should not touch the through hole, only the back centered hole or adapter.  Over drill the center so that it does not touch the shaft.  If that is correct, then the actual shaft size should be matched to an adapter ring.  The prop ring centers the back of the prop hub and prop nut and washer clamp the prop against the adapter.

[john e. holliday]

For years since I was told about them is the use of a plumbers pipe reamer.   I still use them.  Take it slow going from the back first and then the front.  When I get close enough I put them on the engine and tighten.  Some times I may have to do another twist or two but strive for snug fit.   I think Mr. Meriwether put me onto the pipe reamer back in the days of the Flying Eagles of KCK.

By the way I do have both of the step reamers and quit using them.

[Allan Perret]

If you have a drill press and some scrap hardwood, you can make a simple jig to center prop relative to the larger bit and clamp it while drilling.  Explanation would be rather lengthy.  Will take a couple of pictures next time I get into the shop if you can wait.  Method might work a little better if you get a shorter than normal bit, McMaster-Carr sells them, 8947A128 is the 5/16" w/118°point which has less tendency to self-feed vs the 135° when enlarging an existing hole.  You can also regrind the bit to a lower clearance angle to further minimize the self-feed.  This method is commonly used for drilling plastics.   

[Dave Harmon]

https://www.apcprop.com/technical-information/technical-support-advisories/

If I interpret correctly, the through hole is not reliable for center or balance, and the shaft should not touch the through hole, only the back centered hole or adapter.  Over drill the center so that it does not touch the shaft.  If that is correct, then the actual shaft size should be matched to an adapter ring.  The prop ring centers the back of the prop hub and prop nut and washer clamp the prop against the adapter.

You've got it!
One thing though....that procedure is for much, much larger props than we would EVER use for any c/l size engine or electric motor.
For prop sizes we would use....an adapter ring to fit the shaft is not included or needed however, if your prop comes with an adapter follow the link Fred has posted.
For C/L sizes....again....use a tapered reamer from the rear and ream until the front edge of the hole fits just snug on the shaft.
Mount the prop on the engine....the rear surface of the hub will square the prop against the engine drive washer or spinner back plate while the front of the hole will hold the prop on center.....because it is snug on the shaft.
NEVER ream from the front of the prop or you will lose the center.....always ream from the rear.
The hole is too small....that's why you are reaming it....so ream the front of the hole from the rear slightly larger...take it easy....this works as APC intended.
There is no reason to do this by any other method.
This is not ME talking....this is the APC method

[Serge_Krauss]

Thanks for the super replies, guys! You've given me some insight into  a lot of machinist techniques and tools. Much to digest and the right approach to take. While I mull this over and perhaps get a reamer, I can bypass this step in my "house that jack built" project and still center the spinner to finish contouring the nose. Then I will be able to afix the prop and fit the spinner to it. So, thanks much for explaining the various aspects to me.

SK

[BillLee]

The cast-in hole, as pointed out above, is the accurate component, and any drilling or reaming or ... must be indexed off of it. I even question the contention that the back of the drilled hole is where it belongs, too many seen where it appeared to not be.

When I worry about this, I index the prop in a milling vice so that the cast hole is centered under the chuck of the mill, then use an end mill of the proper diameter to make the through hole. Any drill bit will want to follow the existing hole, the end mill will stay true.