Hi all. I have the PDF that denotes the dimensions for turning the shaft down as well as keyway size and placement.  I am not a machinist but I have a lathe, Bridgeport and a bunch of other fun stuff, however I can make and fix parts. So I am going to do this myself, not yet, just planning ahead but stuff like this keeps me up at night.
Here are my questions:

I have an AQ shaft. What cutters are you guys using. I am thinking carbide inserts for the lathe which I have. Is it a pain to turn down this shaft. How does it cut.
The PDF image shows the keyway be in the same line as the impeller machined keyway.  How are you guys setting this up in the mill. Are you putting a key in the keyway for the impeller and then indicating off of that with a precision ground block or something. Also what cutters are you using (size and carbide or HSS). The key is .250 but I imagine cutting a couple thous less than that. The machine handbook shows what depth I need for the key so that should be standard.
Thanks.
T.J.

Do you have enough room between your chuck and live center to chuck the bowl bushing diameter in your chuck jaws and center the splinter end in your live center?  The 1-1/2" diameter doesn't run true, so don't try to chuck on it unless you have a 4-jaw independent chuck that you can indicate on the impeller diameter.

If you already have insert tooling tooling, I highly recommend picking up some inserts that are the appropriate grade for stainless and high-temp alloys.  Otherwise, you can get a left hand cemented carbide tool from McMaster-Carr.  I used some generic multi-purpose inserts at first.  Probably, whatever carbide insert you have will get you through cutting one shaft.  Just use a tool with a 1/64 radius.

They all cut different depending on which shaft you have.  The American Turbine shafts cut pretty nice.  Other brands tend to have hard spots and/or chatter a lot.  With my good Iscar tooling, I run the Iscar recommend axial depth of cut and speeds & feeds, but with the cheap generic stuff, I run 256 RPM, .008 IPR (to start), while taking .035 off the diameter and I brush on a lot of Tapmatic #1 Gold cutting fluid.  Heavy cuts or not using cutting fluid builds a lot of heat in the material, causing it to expand as much as .003 on the diameter.  Just make sure you let the part cool before measuring for your finish cut.

If you run into hard spots, try a cutter without any nose radius with just a couple thou axial depth of cut and a feed around .0015 IPR.  That usually works for me to salvage a nice surface finish.

If you don't have a shouldered wear ring, cut .080 off the impeller shoulder before you cut the 1.371-1.372 diameter by 3.750 shoulder for the inducer.  This will allow you to achieve a .035 front clearance on your impeller.  Make the .080 cut to 1.250 diameter.  It will help the shims and impeller register better on the shaft.  You might need to cut more than .080 or you might need impeller shims to arrive at .035 front clearance.

I set up the shaft in one of the T-slots on the mill table after indicating the center of the T-slot.  I like to line up the slots, but I really think it doesn't matter.  Some argue that the shaft will be stronger if the slots are NOT aligned, but I don't buy that.  I think aligned looks better.  Eyeball the impeller keyway to the 1/4" end mill you are using to cut the keyway before you tighten your hold-down clamps.  You can also hold the shaft in a vise and use an edge finder.  Whatever works best for you.

If you nailed the 1.371-1.372 diameter, touch off on top of that diameter and cut the keyway slot .120 deep.  I locate the slot .160 from the front surface of the inducer and back to 2.750 from that same surface.  That centers the keyway in the inducer fore/aft.  Inducer keyways are not standard.  Give your keyway a little clearance.  It sucks having to beat it apart later.  A nice slip fit (.002-.003) is what you are after.

You are going to need a carbide end mill.  I have been running the 1/4" Data Flute SSI-4 with C-11 coating.  I run them on the Bridgeport at 1115 RPM and ramp down into the part with a .035 axial depth of cut each pass.

If you want to be really bitchen, turn the shoulder .440 longer to move the inducer forward, then make a spacer to go between the inducer and inducer spacer.  The stack of inducers and spacers should be .010 longer than the shoulder turned into the shaft.  This is so the inducer is captured (with crush) between the impeller and shoulder.

Cheers,

Joe

Thank you for the kind words.  I always like to do anything to promote the machine trades.  I encourage pushing your abilities as well as your knowledge of quality tooling.  We have a saying in the machine shop, “Your toolbox is your resume and your job security is only as good as the last part you made.”

My current thinking on inducer design is that a jet boat inducer should be treated more like a screw propeller rather than an open axial flow impeller.  There are, however some subtle differences.  An inducer does not directly contribute to propulsion.  Should the impeller be removed, the inducer by itself would not produce any thrust.  The sole purpose of the inducer is to feed water to the inlet eye of the impeller at a higher rate than it can draw in on its own.

Particularly at the launch out-of-the-hole, our mixed flow pumps struggle to recover.  The more horsepower the engine produces, the faster the RPM increases; the centrifugal forces acting on the volume of water, contained within the vanes of the impeller, is discharged faster than it can be replaced.  This brings me to one of my favorite sayings, “You can’t push a chain or pull a liquid.”  If you try to push a chain, such as in raising a bay door, the chain will just bunch up and do nothing.  Pulling on the other end of the chain removes the slack, force is transmitted from one link to the next, the door mechanism actuates, and the door rises. A liquid is the opposite of a chain.  There is no mechanical link between the water molecules.  The water discharges from the impeller so fast that an air bubble is created at the impeller inlet eye.  Any water that does make it into the impeller is quickly discharged.  The pump never properly loads and the engine free revs until it bounces off the rev limiter (if so equipped).  Ergo the impeller needs to be force-fed with water.

There are numerous ways to load the impeller including a dropped keel, loader, and shoe, but we will limit it to just the inducer because the others require the hydrodynamic action created by the forward motion of the boat.  Currently available inducers provide the most dramatic results out-of-the-hole.  To realize why that is, we need to first evaluate the current design.  Using a propeller concept:  the three most significant characteristics of a propeller are diameter, RPM, and pitch.  In a jet boat, the first two characteristics are pretty much defined for us.  The confines of the suction housing limit the inducer diameter.  The RPM is defined by where the engine makes peak horsepower and the corresponding cut of the impeller.  The presence of an inducer has no influence on RPM.  Pitch, the final variable, is the only remaining characteristic.  The pitch of a propeller is described as the distance the propeller would move axially in one revolution, should the media that it is screwing itself through, be a solid instead of a liquid.  Currently available inducers have a pitch of approximately 5.184 inches per revolution.

I have constructed a simplified table comparing various RPM and MPH to relate theoretical distance the inducer, theoretically, should be pushing the boat forward relative to the actual distance the boat moved forward per second.  Unlike a propeller driven boat, since the inducer has no bearing on how fast the boat actually moves at any given RPM, we see that the inducer, at some point, becomes a restriction to flow.  At this point, the keel is providing the greatest loading affect.  The velocity of the water feeding the pump, from the forward motion, exceeds the pitch of the inducer should it be pushing the boat forward should it be a propeller. Numbers in the chart greater than one indicate that the inducer is working to load the impeller.  Numbers less than one indicate where the inducer is a restriction to flow.  One is theoretical “neutral” where the inducer is neither hindering nor helping to load the impeller.

Moving the inducer forward .440” is the furthest forward that the inducer can be moved before hitting the hand hole cover.  My theory for why this modification works is that it opens up the area between the impeller and the inducer.  Once the inducer becomes a restriction, flow through the lower portion of the suction housing becomes more predominant as the majority of flow is now passing under the inducer rather than through it.  The most noticeable difference will be apparent in the fastest boats.

My opinion is that if you are paying to have the work done and are on a budget, the money is best spent on something that will provide the most reliability or performance per dollar spent.  However, if you have your own machines and are doing the work yourself, this is an easy little project that can provide a performance benefit for nothing but a little of your time.  Just make sure that the inducer has .010” crush between the shaft and impeller so that it is positively captured and does not rattle around on the shaft.  That means that the shoulder turned in the shaft should be 4.190” long and the combined height of the inducer and spacer(s) should be 4.200”.

You are only limited by your time, your talent, and the depths of your pockets.

Cheers,

Joe