Hi,

Have you ruled out a suitable steel tube?

You could solder/weld the extra bits on.

See Jason’s work for ideas.

Good luck.

Bear….

If I can do that sort of thing on my Imported lathe then a Myford should be able to do it too. However an ML7 could possibly be showing it’s age so a bit of a tapered bor emay result.

You will certainly need a fixed steady as having that much metal sticking out of a chuck is not practical or safe.

Drill out a smuch a spossible using “blacksmith” drills which have a reduced diameter shank so can be held in a tailstock chuck or pick up some old MT2 shank bits and sharpen them, doe snot have to be perfect as you will be boring after drilling out to 1″

As for a boring bar the choice is yours Carbide insert in which case use CCMT 09T302 inserts which are sharper than CCMT. Or make your own from say 22mm bar, drilled at an angle to take a 1/4″ HSS round tool bit and cross drilled & tapped for a grub screw to hold the bit. Clamp bar direct to cross slide or even remove that and use a solid block fixed to te cross slide.

If you could put the fuse in to the opposite end then the possibilities for between centre boring bars which are likely to give a more parallel bore should be considered.

Never tried this particular job, but a couple of observations.
I’ve been out the the garage and can only just fit a 50mm bar into my Myford fixed steady, which is well worn.
A new one might need replacement fingers, though large bore steadies are available.

50mm OD 40mm ID tube is available, seemingly for hydraulic use, so maybe a scrapyard/hydraulic ram refurbisher would have something available. One end might even be already welded closed.
New tube is available, just as an example; other sources my be cheaper or closer>
https://electrohydraulicscontrols.com/product/honed-steel-tubes-size-od-50-mm-id-40-mm-per-meter/

Cutting Edge Engineering regularly shows videos of modifications of hydraulic rams & cylinders, albeit at a larger scale.

Not all golf balls are the same size, as only the minimum OD is specified (1.680 inches 42.67 mm)
https://www.randa.org/en/roe/the-rules-of-equipment/part-4-conformance-of-balls#43-size

The bottom of a blind hole might not need to be flat if the “piston” is spherical

If you can borrow a second fixed steady, then that could possibly be used to support a large diameter boring bar as it enters the hole. Depth of cut could be adjusted by moving the boring insert, rather than the cross slide.

Bill

Perhaps you can find some sort of hydraulic cylinder of the right bore and cut it short. I’m assuming you are making a pump or something not an actual mortar, even as a firework or starting gun is illegal without the right licences.

On 26 January 2026 at 18:08 joebouy Said:

..might be willing to share their insight and experiences

If you want people to share their experiences and help you, please have the courtesy to link to the thread you have started elsewhere.

Then people here would learn of the suggestions you have already received (this saves repetition). This saves repetition. They might also learn from those suggestions for their own projects.

https://www.practicalmachinist.com/forum/threads/is-this-possible-on-a-ml7.445963/

5.5 inch deep hole at that diameter is no big deal. As Jason said  drill it then bore with progressively larger bars, either insert or HSS. No need for solid carbide or exotica.

If you get a bit of vibration or chatter,  a lot can be done with wrapping strips of rubber inner tube around the job to dampen it. Common practice on reboring large  hydraulic cylinders on old worn out lathes.

My ML7 will drive a 1″ drill easily at about 200rpm  ie low speed but not back gear. MT2 will not slip if seated firmly. Whack it with a brass bar or copper hammer . Drill a pilot hole first and then 1/2″ before the 1″.

Fwiw Joe and what I learned with my own 1/6th scale Napoleon 12 pdr project. For it and because I hate continual polishing of brass or the correct bronze, I chose 303 stainless for the barrel and all other metal. I’ll need to mix a bit of imperial and metric measurement units though. For the correct scale bore size, my barrel needed a 20 mm bore for nominal sized tooling, that’s not 100% to exact scale size, but still within a very few thousandths, and just over 266 mm deep. Obviously it’s highly desirable for safety to have the barrel O.D. as concentric as possible to the bore. So start with an oversize barrel blank for diameter and length, then fully finish the bore first.

To do so, I started with a good accurate center drilled location, rough turning a location for my steady rest fingers, then a normal jobber length 3/16″ drill to about 1/4″ deep. I then single point bored that to as close to 1/4″ diameter as I could measure. That now round and precise short bore helped guide a jobber length 1/4″ drill to it’s full depth much like a drill bushing would. Because of the center to center distance of the smaller lathe I was using, I had to then transfer everything to my floor model drill press. Indicating all that back in and step drilling about 5 more times, using extra table supports down to the floor for gaining extra table rigidity etc. I then used a 12″ long 1/4″ drill to full depth. From that, I started using a 1/2″, then 3/4″ extended length drills. That ridiculous impracticable set up and the drilling took just about another 5 hrs to do. But I can say that all drills should be of high quality and extremely sharp. This isn’t the place to cut corners !!!

For a smooth bore black powder model, no great accuracy is needed since you’d still be patching the projectile much like a black powder rifle might. I’d think even more so with golf balls since I highly doubt from brand to brand the exact diameters are held to very tight diameter tolerances. For myself I considered two choices, final drill with a proper 20 mm drill, or make a 20 mm D bit reamer. I took the easy way and drilled. In hind sight, drills don’t leave a great surface finish and most likely the D bit reamer would I now think have been the much better choice. It’s the one place I really should have done better.

If you chose to go that route, I’ve recently read but still can’t say for sure that at least .005″ – .008″ should be left under size for a D bit to produce a decent finish and straight hole. If too little is left, the D bit will tend to follow any drilled hole which may not be all that straight.

With the bore finished, you then need to check how concentric it might be to the barrel blanks O.D. To do that is actually quite easy. I simply used a long length of 1/2″ round stock, drilled and tapped very close to the end for a short set screw. I then turned the set screw end to a point and threaded it through the end of the rod until it’s point was protruding. Hold the rod angled slightly up in a bench vise with that set screws point up. Slide your barrel blank over the rod until it then stops against the bottom of the bore. Now set up a magnetic base and with the dial indicators tip roughly where the tip of that set screw should be. Zero the indicator, then slowly rotate the barrel. Even with all the effort I took, I found I still had about .063″ of run out. Mark the barrel blank with a scratch mark or felt tip marker for either its highest or lowest number and how much and in which direction it is. For a drilled hole 10 – 1/2″ / 266 mm deep and mostly drilled using a drill press and not a lathe, I considered my final result as not too bad. I still think I got a bit lucky and certainly wouldn’t bet I could repeat that again. But the initial single point boring to help guide the first drill was a huge help. I’d still do the same again even now while having larger lathe with enough between centers distance.

With the off set number and the bore position known, I then offset the end of the barrel blank to that known bore C/L and center drilled it. Using the top slide to then turn a very short and narrow 60 degree land at the muzzle end will then allow turning the barrel blank between centers.

Again it isn’t exact scale as the barrel trunnions would have been cast integral with the barrel. But I step bored each of those trunnion positions, then drilled and tapped to within about .100″ of the bore. Depending on if your using a scale drawing of what you want, some trunnion C/L’s are located on the bore C/L, and some were purposely offset to have the top of the trunnions pivot at the same elevation as the center of the bore. In my case, the trunnion C/L’s are centered on the bore which made it a bit easier. I hope some of this might help.

But to use a full size Napoleon 12 pdr barrel for bore size and length. From my own reference material and in the 1860’s, they were boring these barrels to around a 4.72″ bore a bit over 60″ deep, with at best high carbon cutting tools and some fairly rudimentary machine tools. I’m unsure about land based artillery, but I know for a fact that at least the north had naval inspectors using for the time quite high precision go-no-go gauges for smooth bore ship board artillery. Surprisingly to me those gauges allowed checking to under .001″ before any barrel was accepted and paid for. And while they weren’t blind bores, the then new and rifled Armstrong artillery pieces had even much longer bores. Few real details about how all this was accomplished back then seem to be easily available. But I suspect an extremely close fitting and sliding bushing the boring bar gained support from as the bore was deepened. It’s about the only method I can think of with the available materials, machine tools and cutting tool technology they had at the time.