.Not trying to upset anyone but I find the heavy cuts and feed rates for carbide not always true, I use ccmt060204 and dcmt and rcmt inserts both standard and polished and find fine cuts just as successful as deep ones. On the question of boring in the mill it’s possible to rotate the boring bar in the head where on the lathe the boring bar has a flat on it giving positive location could that be part of the problem?

A sensible observation. My workshop rarely allows the fast heavy cuts typically needed to optimise carbide. I mostly work on fist sized objects using not particularly fast, powerful or rigid hobby machines. Difficult to get high surface speeds on small diameter work, so sharper carbide inserts often cut better than blunt efficient ones.

Boring is on my list of difficult operations. The biggest problem I think is boring bars tend to flex and chatter because they have so much overhang.

For convenience I prefer carbide boring to HSS, but getting good results can be fiddly, maybe swapping inserts, and often having to try different combinations of RPM, Feed Rate, and Depth of Cut. Fast and light cuts generally, but much depends on the material and the depth and diameter of the hole. I find it easier to get good results on larger diameters and deep holes are harder than shallow.

Dave

Boring on the lathe, with a boring bar in the compound slide on a small (not very rigid) machine is never going to be straight-forward. Problems are further increased with increased depth of bore, not diameter. I would never countenance using the compound slide as a means of extending the boring bar.

Mounting the part on the carriage and using a boring bar (supported at the chuck and tailstock) can clearly reduce the number of flexing joints in the process. So far better for deeper (longer) bores, but a pain to set up, of course. I’ve never yet needed to make a boring bar of that form.

Boring on the mill allows shorter cutter extension, so is inherently better than on the lathe – the only real mounting problems being for awkward shaped items. Knee raising is, IMO, better than quill extension when boring (both my mills have knees, but a fair amount of head-space is needed, so I haven’t used the smaller one for boring).

On the lathe I first drill, then bore (if a larger size) – followed by a reamer, if I have one . So much less hassle for most holes.🙂 Much like Howard’s post above.

Mike, sorry to hear of your difficulties. Are you 'missing something glaringly obvious?' Well, I can't tell, but you've left the door open for folk to risk insulting you with the basics…

it's nothing like as easy to set a boring bar's position with respect to the work as it is to set a lathe tool for external cutting. For a start, it's difficult to see what you're doing. A major risk is that there's interference between the bore and the bottom of the tool tip – obviously worse as the bore diameter decreases. We always try to stuff our thickest bar into the workpiece, so that's increasing the risk. It's often necessary to gain clearance by setting the tool at what looks like a horrible negative rake. Raising the point of contact so that it's a tad above centre height is also a good idea. I find it much harder to set a tool correctly in a boring head, but the geometry is the same.

I recently bored several bits of an unfriendly stainless steel (dunno what exactly) using an Emco Compact 5 and Arc Euro's no-name **MT and **GT inserts. Bore dimensions similar to your job. To be honest, I didn't expect much from such low-priced inserts, of unknown provenance, and used them as an experiment, reasoning that there wasn't much to be lost. They did the job splendidly! The Compact 5 is not the world's most rigid lathe, but the resulting bird's nests of stringy swarf were witness to the fairly serious cuts and feeds used (sorry, I can't quote any figures…). I can only think that success was due to the lathe being in good condition, and the careful setting of the tools.

Mike, investing in a couple of "blacksmiths" drills (reduced shank) would be worthwhile as at 13mm the largest insert bar you could usefully start with would be around 8mm shank and at 55mm deep you are close to 7xD sticking out of the toolpost which is going to flex and chatter.

I really only use something like a 6mm bar mentioned above for small holes say taking a hole drilled 11mm out to 12mm finished size as the diameter of the job goes up I just used a larger dia tool and would only be using 5 thou cuts to finish things off 20-30thou to hog out the majority of the waste on the Chinese hobby machine.

If the finish REALLY matters, rough out, leaving slightly undersize and finish with a cylinder hone ! Noel.

Tim,

Almost certainly, we each have a stable containing at least one hobby horse that we ride from time to time.

I certainly have!

Howard

You would be unlikely to be able to go straight in with a big one but working up in 3mm or 1/8" steps it should cope with at least 20mm.

I have the 1/8 "increments upto 1" and not any special quality and just work my way up in size which is generally quicker than trying to force a big one in from the start. Good enough to quickly remove metal so you can get a half decent sized boring bar into the hole. This was drilled to 7/8" (22mm) and then bored to the final 24mm.