I want to make this caster barrel, material is steel DOM tube. I’ve made a previous version on a manual lathe w/ a 4-jaw, and flipping to do each end. While it worked, it was a pain and I didn’t get the two seats as close to concentric as I’d like.
The two 1.375” areas are bearing seats that need to be as close to being on the same center as possible, the rest of the dimensions are clearances that are less critical.
I’m working on teaching myself Path Pilot, but before I try to recreate this in PP, I’d like to know if it is actually possible to do it in one setup. The question is if there is a boring bar or other bit that can make the 1.375” seat cut on the chuck end? (cost is an issue….) I could certainly do it by flipping the part but I really hate zeroing in a 4-jaw, and would rather only have to do that once per part. (I’ll be making about 6 of them)
We have two 15L Slant Pro’s, one w/ a turret and one w/ a tool-post to pick from, not sure which would be better…
Boring bar rigidity at stickout is always questionable IME, but for 2.5" you could probably get a beefy bar that would hold ok. If you don’t need a perfect right angle step it would make life easier as you could use the same tool to do both bores in the same op.
If your OD is consistent you could also bore some 3J soft jaws to size and flip the part vs dialing a 4 jaw all the time too.
The bearing is a 99502H, and it needs to sit on the step pretty solidly… It has a ~0.2” / 0.6mm radius corner, so a matching radius on the inside of the step is OK, but it needs to be a right angle otherwise…
Looking on Amazon, I found this “Internal Grooving Tool” that looks like it would cut at a right angle in both directions if it can be used to cut in X as well as just making a narrow slot… Would something like this do the job? The carbide insert sticks out far enough that it could definitely cut both steps, though possibly not quite far enough for the clearance area (depending on which end I started from) However I could always to that later in a three jaw since it doesn’t need to be perfectly in line with the seats… It has plenty of length to go full length, so I could imagine doing the entire job with the one tool.
I don’t have any experience with that particular tool, but many grooving tools and inserts don’t do well with axial cuts like profiling, so that could be an issue.
You could use that to cut grooves where the steps are and do the rest with a typical profiling tool.
If you were going to do a lot of them (depending on the application), it might be easier to get tubing with the 1.375" ID and press/shrink/glue in a spacer.
That is absolutely doable in a single setup, but tooling is going to be the deciding factor. If cost of tooling become prohibitive, a collet chuck would probably be a better option than a 4-jaw so you can flip the part without worrying about dialing it back in.
Assuming an appropriate tool or tools is not in the budget, I think my approach would be to use a 3-jaw with the raw bar to turn the OD and as much ID as possible, then part. Do this for all of them. Then swap to a collet chuck with either a step collet or an ID expansion arbor and finish the other side of all of them. That should get you good concentricity and easy setups.
I’ve always thought it was doable in one setup if I can find the appropriate tooling… I suspect that part of my issue might be that I’m not sure what to call that sort of cutter / bit when I’m entering terms in a search engine I’m sort of surprised it doesn’t exist in more common uses as I can’t believe my use case is that unusual.
The collet chuck is somewhat of a problem (I think) because we only have a setup for 5C collets, which only run up to about an inch, as my tube is 1 3/4” OD…
I can see how Ian’s suggestions, would work, but if I can get a tool like the one I linked above I suspect it would be less expensive than some of the things he suggests.
You’re looking for a boring bar, and/or an ID grooving tool. Boring bars often have a bit of a forward rake which won’t allow you to get the straight wall you need for the far bearing pocket, this is where the grooving tool comes into play.
As for the 5C collet, you’re right that the standard collets only go up to an inch, but you can get step collets in larger sizes. They are typically not hardened (or at least, not in the gripping region) so they can be machined to an exact size if needed. Alternatively, you can get 5C ID expansion arbors that will grip the existing bore while you finish the remaining bearing pocket.
I’d get some soft jaws for the 3-jaw chuck and bore them to size and skip messing with step collets. They’ll hold at least as true and can be recut to do other things later if desired.
The makerspace has two 15L’s one with a turret and one with a toolpost. So no reason I can’t use two tools…
I haven’t had much luck so far finding a boring bar that can do the back-bore. That grooving tool is the only thing I’ve found so far. I can see how it might not do well on an X-axis cut, however I’m wondering if I could make repeated overlapping Z-axis groove cuts to almost full depth and then do a shallow (say 0.005”) finish pass in Z to clean it up? If I did the tool path to do the end with the most material removal on the tail end I can do all of that end with a shorter conventional boring cutter, and only need to do the short end with the grooving tool…
I’d add that a secondary advantage of doing it with the grooving tool is that it seems like that would be the easiest method to repeat at some future point (possibly with a variation on the dimensions) without worrying about re-zeroing any other fixturing….
Two tools is almost definitely going to be the way to do this. Your thoughts on the grooving tool roughing and then doing a light X pass probably would work, but depending on the tool, you might find you get really poor tool life. Maybe that doesn’t matter though?
I would do everything with a boring bar, then come back in and finish the wall of the rear pocket with the grooving tool. Or, use the back facing style of boring bar that Daniel posted, but you’ll still need a standard one for the front pocket wall.
All said and done, there are a lot of ways to do this, but the old cheap/fast/good adage applies so you need to decide what your priority is. Cheap/good is one tool, multiple setups.Fast/good is multiple tools and one setup. Cheap/fast is one tool, one setup, but possibly destroying the tool and/or making bad parts.
Yeah, use the grooving tool to put in a groove where you want the square corner and any other profiling tool to do the profile. It shouldn’t matter if the groove is slightly too deep as you’ll have plenty of material to hold the bearing.
I’m sort of surprised it doesn’t exist in more common uses as I can’t believe my use case is that unusual.