What does your team do to cut aluminum shafts to length? Our team normally uses a bandsaw to within 1/8” and then sands the rest to length, however we find that this is quite slow. We have a lathe that we haven’t used in a while, maybe this would be more precise?
If you have a cutoff tool and a through chuck for your lathe that’ll be the best way. you could always cut on bandsaw and trim to final length on the lathe. would be faster than sanding at least.
A lathe will be more precise.
Do NOT extend the shaft beyond the left end of the head. This is not safe!!
So, if your lengths of shafts are longer than than the head length, you may need to find a bigger lathe, trim on a milling machine, or go back to sanding.
Yes, I know experienced machinist can, and do, extend parts beyond the back of the lathe head, but is not something for beginners to try. Please don’t do it!
I’d also recommend bandsawing closer than 1/8" if you can. -much less sanding!
I see you, I agree it requires additional attention. Obviously there is a length that is really unsafe, however I will have to disagree. The through bore of the head is there for a reason, you can keep things under control and safe easily enough, relatively new folks can still pull this off easily enough.
Yes, use the lathe. More specifically, face both ends of your shafts leaving the shaft oversized, then measure your shaft with calipers (or a mic if you really want to). Put the shaft back in the lathe and zero your tool to the exposed face, then just remove the excess material. Get a DRO if you don’t already have one, it will make your life much easier, and they are easy to retro fit to most lathes (at least on the long axis). Cut off tools are great for short spacers or shaft because you won’t have to do any measuring off the lathe, but be careful not to get too much material stickout.
A mill can also be good especially if yours is setup well for long thin stock. We have 3 small vices on ours for tube and shaft work.
Hacksaw to +1/8, face the ends and face to final dimension is the most consistent/ least fiddly way on the lathe. Cutoff tools are generally not newbie friendly and can be really fiddly to feeds and speeds. facing is far more forgiving and there is less going on.
Bonus points for the lathe ease of tapping the shaft by hand (power off, in neutral, tap in tailstock)
Harbor freight used to sell this and it’s useful for it’s length capacity. It’s at least consistent and repeatable, and makes a great “tool” for learning vernier scale.
ALUMINUM 24" IN/OUT METRIC/SAE RULER WITH CALIPER Amazon.com
To be clear, this is useful to measure long axles outside of the lathe. You take your measurement, write down the delta then chuck it up and zero your smaller caliper to the material stick out and cut the delta.
Then do whatever turning down for bearings or snap rings, etc.
Keep the RPMs down if you got a lot sticking out the headstock. It’s just aluminum, 600rpm works. I’ve never seen a problem with a 7" lathe, personally.
+1
We have a lathe but don’t really know much about using it/haven’t used it in a while. Chop Saws or Miter Saws work pretty well for the tolerances that we need. We usually have an extra person help hold it down or use clamps depending on the length
I have had pretty good luck with the HSS ones, but I have only had a few and I have primarily used them on brass and aluminum (next to no steel, definitely not anything beyond mild steel). I can’t speak to carbide, nearly broke undergraduate Skye with a hobby lathe in the garage couldn’t afford a whole lot of tooling.
Consistent feed pressure kept them cutting well, they weren’t fans of restarting a cut. (i.e. hex shaft might be rough without turning off the hex portion)
Parting in the lathe is the fast way to cut and face hex shafts. The tricks are to have the parting tool stick out only the radius of the part plus perhaps 1/8" so the toolholder does not hit the part, to make the cut right next to the chuck with only enough clearance between the toolholder and chuck to avoid a hit, to maintain a dribble of WD-40 on the cut, and to set the tool just a hair below center. These tricks help ensure rigidity, which is the key to pretty much all successful machining. Of course the tool needs to be sharp and have front clearance. Keep up a steady feed that makes a chip thicker than, say 3-4 thicknesses of paper.
Only grind the front of an HSS cutter. If you grind the top or worse, the sides, then the tool is fatter behind the cutting edge and will jamb on the side walls of the groove being cut.
We part, face, and chamfer one end (cutting a snap ring groove if that’s in the design). We then remove, measure, figure out how much length has to come off the incomplete end, put the part back in the lathe, touch off the unfinished end with the DRO, move over a little less than the amount to come off, part, possibly remove and measure again if high precision is needed, face the rest, chamfer, and groove if needed. A 60° rather than 45° chamfer is prettiest on hex stock. That’s what is typically used on factory-made hex nuts. Check one out and try to copy that appearance.
Ah, that’s the tricky part though, right?
Is that unsafe length 3"? 10"? 5x the material diameter? 20x the diameter? Is a centering collar being used? What is the spindle speed? What is the material? Is the material bowed or straight? Etcetera.
Every setup in a machine shop has some level of expected safety, or un-safety, if you will. One of my daily goals is that everybody goes home with the same amount of blood they came in with. By having an easily defined amount of material allowed to stick out (zero) my daily goal is much easier to achieve.
Sure, but saying “never ever do this” without an explanation why is a) catnip for people on the internet b) less helpful in building the knowledge to identify safe/unsafe behaviors.
You could, if you wanted to, calculate ballpark numbers using shaft whirling equations (Drive Shafts Critical Speed - Roy Mech) and determine an upper bound for stickout. Personally I’d say “minimize sticking out the back and ramp your speed gradually, if you get any wobble stop and asses your setup for safety” That way you’ve told them the risk (whipping of the shaft on the back of the lathe) in a way that also reminds them that having too much of the shaft unsupported in general is maybe unsafe and you should evaluate that.
Honestly, I was pretty sure what you were worried about but was like “wait, amAndyMark I missing something dangerous aside from that?”
I generally share this goal.
It may be easier but zero stickout may not always be an option and teaching the specific why your goal is zero is helpful in thinking about how to make sure everyone keeps their blood on the inside where it belongs.
Let’s back up a little.
My first reply to the OP is based on the presumption (perhaps erroneously) that they have little to no experience with a lathe and there isn’t somebody on the team with the necessary experience (or they would have asked them). With that in mind, I stand by my statements.
Yes, this program is about education and I could have given a lengthy explanation on how to make the setup safer, but I think that would require questions that needed to be answered first: Lathe size, desired length of shaft, diameter, etc. Even then, I wouldn’t feel confident about the setup and safety without being present to actually see it.
I could have said do not stick the material out more than 5x (or whatever) the diameter of the material. But what if that still isn’t long enough to make their shaft?
So, my easy (safe) answer to a newbie, that I can’t help directly, is to reduce the chances of them getting hurt.
You’re right, I probably should have given reasons why sticking material out the back of a lathe head is unsafe. So, here’s a true story…
I was working in a machine shop in the early 80’s (so I don’t remember all the details). The shop owner’s father was working on a smaller lathe, maybe a 8-9" swing. He had his material, something around 1/4" -3/8" SST sticking about 24" out the back of the lathe head. He turned on the lathe and I hear: whump. Whump whump. Whump whump whump whump. Faster and faster in about 2 seconds. The rod bent 90° and made an even louder whumping sound as it whipped around. I ducked in behind a heavy work bench for protection. The material pulled out of the 5C collet and stuck into the plywood ceiling about 20’ above us. We were very lucky the rod went up. It could have gone in any other direction and maybe killed somebody.
It was a new setup for the dad. He had been previously working on something else and left the spindle on a high speed. He knew to run it very slow, but forgot to put it in back gear. People make mistakes, I get that.
Now, we know that 24" was too much to stick out. Again, I ask what is the safe amount?
I have stuck material out the back of a lathe. I have allowed students to do the same, but we now have a teaching moment and I can explain why, why not, how to, best practices, options, safety, etc.
For most hex we end up using our miter saw with a dro for accuracy but in the 2022 season a handful of our shafts where cut on a bandsaw then cut to an accurate size on the mill but that was slow and not a worth while process
Old favorite: match drill a metal yardstick to the fence on your miter saw, attach with countersunk screws. Obviously this needs to be pretty precise when you initially set it up, and will only work if you always use the same width blade. We used a setup like that to consistently hit +/- 1/32" on box tubing for several years, Diablo non-ferrous blade iirc.
Our typical process is to cut close to length on the horizontal bandsaw, face both ends on the lathe, measure with calipers, and then face to final length on the lathe.
As others have mentioned, already having the part on the lathe makes it convenient and easy to end drill and (usually) tap the shaft with high fidelity.
Strictly speaking this is generally far more precision/accuracy than is actually needed, however, having parts that just fit right makes assembly a joy rather than a chore.
Please note that we have access to large Clausing Industrial lathes so any shaft we are ever likely to cut won’t be long enough for the left end to stick out through the headstock. Nonetheless we turn slow and cut lightly.