Author Topic: Well that was boring...  (Read 1209 times)

Offline Joules

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Well that was boring...
« on: June 24, 2018, 08:16:18 AM »
Another deeply roasted job from being on the back burner for over a year.  I made up a tool holder with a Foredom rotary hand piece to drill and light duty grind in the lathe, it can be powered from the Foredom flex drive or a small motor fitted on the back for a more compact unit.  The tool holder has a 1" bore and I have since bought a few more for other tooling. 

Whilst mulling this over I thought, a key slotter/lathe shaper tool would be cool, so I went searching for bearings.  I came up with some 1"x3/4" bronze flanged bearings, ideal thinks me.  Then tried them in the tool holder.....Errr, no go.  On close inspection the tool holder was very roughly bored, as best I could measure the bore also wasn't true to the outer edges, and my bearing slightly oversize !!!  Bummer.  So it got put on the back burner whilst I figured out how to bore the thing.  Holding it in the 4 jaw was a mare, as the thing had runout all over the place. 

Idiot !!! stick it on the tool post and bore between centres, brill, but I don't have a between centres boring bar.  More rummaging found the 20mm silver steel you see in the parts picture below.  More back burner time, and the smell of hot oily metal passed by.  I got round to making the boring bar and then agonised over what size to drill for the cutter.  Looking though the tooling and junk, I didn't have matching drill, reamer and tool bit.  So 5mm it is then as the drilled hole will be undersized.  That worked, the hole was drilled offset on a small machined flat on the bar, a single grub screw inserted from the side.  The tool bit, sometime later I came across some very hard 3/16" HSS, might have got cobalt in it as it was a bit tough cutting it.  Yep 3/16" in an undersize 5mm hole is still a rattle fit.  Answer, have a beer, now cut the tin and use as shim round the 3/16" bit.

Perfect fit, the tool bit has a flat ground length wise for the grub screw, and the cutter edge is ground at roughly 45 degrees to give a tangential cutting action.  The between centres boring bar was now ready for action.  The tool holder internals appears to have work hardened from whatever gnarly tool they used to drill the thing. The bore also drooped towards the tailstock, so the boring bar had quite a bit of work to open out and true the bore.  Still it was nice to be making swarf with a tool I had made.  Plenty of testing the bearing fits as I opened the bore out very carefully.  The bar will have been flexing so the bore won't necessarily be round, I could feel the elliptical shape inserting the bearing and twisting it being very careful not to get it jammed in.  Use plenty of oil, at this point it was so close and stopped using the boring bar.  The bearings left visible material where they contacted, and used this to hand scrap the tool holder for final fit.  Keep a close eye on both ends so one bearing doesn't wander off centre.

Final fit was done with the little machinist hammer I made a while back.  I was able to tap the bearings in and tap them out using a nylon bar so it didn't damage the bearings.  When finally fitted the bearings are tested with a small bar and rocked to make sure no step bearing to bearing that would indicate the pair not inline, check all round and they seem fine.

And on the back burner again...  No 3/4" silver steel to be found....  :(   Had used it to make other stuff a good while back.

This build is very much ad hoc, no plans and just using parts as I find them.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup: