2011 Dewalt Supliers.

[Bruceb]

So you are saying this is something new? The old ones had a fixed shaft?
Bruce

[Tristan Lall]

Originally Posted by Bruceb

So you are saying this is something new? The old ones had a fixed shaft?

A picture would be useful here, but I don't have any...so I'll try to explain.

The old DeWalt XRPs had a cast metal housing that slipped partially over the gearbox, and extended forward to the chuck. It contained the drive shaft, and retained it with two dissimilar ball bearings (looked like conventional ones; no angular contact or fancy stuff). We (188 in 2006) deviated from the standard NBD plan by removing the shaft, and replacing it with a different shaft that fit within the same housing, but which had a Ø0.5 in keyed shaft instead of the chuck thread and left-hand retaining screw. On the gearbox end of that shaft, we milled two opposing flats on the cylinder (so it looked something like the Ø0.375 in portion of the Globe motor shaft). Those flats interfaced with a little sintered steel coupling on the front of the gearbox, providing a positive connection that was not susceptible to small axial misalignment.

If I'm understanding you correctly, they've replaced the shaft-with-flats with a taper. That ought to work too, as long as you make sure (as we did) to let the shoulder on the shaft transmit the axial loads to the housing, so that the taper doesn't disengage.

[Bruceb]

Well, maybe they didnt change it after all. The shaft, after I took it all appart, is press fit into the bearing and then trapped buy a steel ring behind it that is about .375 wide and looks for all the world like just a piece of steel tube but it only fits on the shaft one way like it has a mating taper behind the bearing.
Tristan, did you use hardened steel for the shaft that you made?
Bruce

[Tristan Lall]

Originally Posted by Bruceb

Well, maybe they didnt change it after all. The shaft, after I took it all appart, is press fit into the bearing and then trapped buy a steel ring behind it that is about .375 wide and looks for all the world like just a piece of steel tube but it only fits on the shaft one way like it has a mating taper behind the bearing.
Tristan, did you use hardened steel for the shaft that you made?
Bruce

That's how it worked on the old drill. The retaining collar was a press fit, and though the inside may have had a taper (I never checked), the shaft itself was straight.

We didn't use hardened steel for the shafts, and that was a mistake. The steel we used (AISI 1018 first, I think, then AISI 12L14) was weak and ductile, and the torque of the drivetrain caused it to twist at the interface with the planetary gearbox after repeated back-and-forth cycling. In retrospect, we should have just used AISI O1 drill rod, and then hardened and tempered it.

[Bruceb]

O.K. I'm not a machinist so how do you harden and temper drill rod after machining it? I think that is what I would like to do as the shaft on the Dewalt does not exactly fit my application.
Bruce

[JamesCH95]

Here's a Datasheet on AISI 01 Steel: http://www.act-on.ca/acton/Steel/Ima.../AISI%2001.pdf

It outlines different heat-treating procedures. Usually one would send parts out to a heat treating shop.

Look at this hardness-to-strength conversion chart for steels to chose the hardness you would like to achieve through heat-treating: http://www.engineersedge.com/hardness_conversion.htm
You'll pick a range for the heat-treater to aim for. My experience with 4130/4340 steel (which is commonly used in high-performance driveshafts) has been that Rockwell C 25-30 is plenty strong with good ductility. If you harden the part too much it will crack before it yields much, and I would much rather have a part yield and still be functional than crack and be useless. If the shaft is experiencing frequent impact loading, a more ductile or less-stiff material would handle those loads better.

@Tristan: why did you (your team) go from 1018 steel to the somewhat weaker 12L14 steel? EDIT: I guess it depends on the grade of each steel, one could be stronger than the other, depending on heat-treatment and cold working.

[Bruceb]

James, is there a steel that would replace the dewalt driveshaft that I can machine and not need to be heat treated? Going to power a swerve drive with it?
Thanks
Bruce

[JamesCH95]

What motor are you planning to connect to it?
What gear (1st, 2nd, or 3rd) do you plan to use?
Depending on your expected output torques it might be impossible to have adequate strength without heat-treatment.


I would consider 6-4 Titanium, 4130, 8620, or 4340 steel.

"But Titanium is so expensive!" -- It's lighter, stronger, and IMHO very appropriate for this application. And you could get a 0.500"ODx36"L titanium bar from http://titaniumjoe.com/6al-4v%20round%20bars.htm for ~$60, from which you'll be able to make many output shafts. It will be a little more difficult to machine, but still very doable.

4130/8620/4340 are fairly inexpensive, not terribly difficult to machine well (get some carbide insert lathe tools though) and has good strength (8620 is the strongest). They can also be welded very easily (ER70S-2 TIG wire is good for these low-carbon alloys) so you could weld on an output gear or sprocket without much difficulty.

[Bruceb]

Sorry all gears using a CIM. Can you lathe turn titanium with a carbide tool?
Bruce

[JamesCH95]

Yes you can. I wouldn't use anything other than carbide! I personally love 3-point carbide insert tools, $20-25 for the bar + 1 insert, and $7 for extra inserts. And each insert has 3 usable faces, so each insert lasts quite a long time. I have also machined titanium with standard carbide tools with good results too. Heavy feeds, slow speeds, and lots of cutting fluid, similar to SS.

[Tristan Lall]

Originally Posted by JamesCH95

@Tristan: why did you (your team) go from 1018 steel to the somewhat weaker 12L14 steel? EDIT: I guess it depends on the grade of each steel, one could be stronger than the other, depending on heat-treatment and cold working.

I originally recalled that it was AISI 1018, but thinking about it some more, it might have been AISI 1045 (turned, ground & polished stock). It was a while ago, so I'm not sure what we actually used.

The AISI 12L14 was used because we had it available, and didn't have too much time to make the replacement shafts (it's a free-machining leaded steel). It was even more ductile, and twisted before failing.

A good alloy steel or titanium alloy would probably work for this application too. Those may well have sufficient strength, without having to deal with hardening—but at a somewhat higher raw material cost. (But hardening O1 or an alloy/tool steel will give even greater strength, if needed.)