Thread: Re-registration of tool bit for a finishing pass?

Say one is turning some mild steel. Tool registration is complete, a number of passes are made until one is ready for a finishing pass or two.
Given a smooth finish is best achieved with a wide tool bit radius and roughing is best done with a smaller tool radius, it probably is best to change the tool bit, but then one needs to register the tool bit again. If the tool bit is being swapped, what is the best approach to re-register the tool bit again, given that probably very little material remains to be removed?

Hi, I always leave 10 or 20 thou on the workpiece, change the tool and then go for a skim cut, measure and finish to size.

To re-register the tip I start the machine and advance the slide until it just scores, you can actually hear it if your workshop is quiet enough. To get even finer adjustment, I use the compound set at + 45 degrees. Surely someone on this forum has messed around with an electronic approach using an LED or buzzer???

Judging by your question it would appear that your not really sure how much to leave for a finish cut.
When you are generally roughing out and using hss what process or procedure do you use if you have to resharpen the tool,
The same question could also be asked if you are using tungsten carbide tips or cemented carbide, what ever method you use for rezeroing your tool just use the same procedure for finishing.

Never used it on a lathe but on the mill when I want to zero the cutter to a work piece nothing beats using a rollie paper.
Just bring the tool down until it grabs the paper and you're within a thou then use the dial scales to move in the last bit as needed.
This works great on both the end and flanks of milling cutters and I can see no reason why it wouldn't work on the lathe.
I don't smoke but always have a few packs of Tally-Ho around the shed.
Cheers,
Greg.

I guess my motivation for starting this thread, was the realisation that sometime a tool change is required for a finishing pass. I typically have just increased the RPM and reduced the feed and hoped for the best. So my thinking now, is roughing cuts and then finishing cuts which may or may not required a tool change. Does not sound like much, but I now approach my turning with one further consideration, one for the better. I just did some testing in the workshop on 2011T6 aluminum using an insert RxMx1003MO (round) for a finishing pass. The big radius made a big difference. Sincerely Tom

Originally Posted by topari

I guess my motivation for starting this thread, was the realisation that sometime a tool change is required for a finishing pass. I typically have just increased the RPM and reduced the feed and hoped for the best. So my thinking now, is roughing cuts and then finishing cuts which may or may not required a tool change. Does not sound like much, but I now approach my turning with one further consideration, one for the better. I just did some testing in the workshop on 2011T6 aluminum using an insert RxMx1003MO (round) for a finishing pass. The big radius made a big difference. Sincerely Tom

At least you asked, we all learn somewhere.

The way was taught is to leave the tool a little loose in the toolpost, I use 0.05mm shim touch the tool on the work with the shim, then nip the tool up zero the DRO or hand wheel then back the tool out and tighten it.

Depending on the job I use a vertical sheer tool which gives a great finish.

This topic comes up from time to time and it's a great one to talk about. One of my biggest challenges I faced when I took up turing was turning to a specific dimension by sneaking up on the finished size. I used to try and do it all with one tool, using an indexable carbide tip. You can imagine all the troubles I had doing that, especially with a tip that was not designed for finishing cuts and would just rub if used for DOC under say 0.5mm. I had heaps of HSS bits and pieces but shyed away from using HSS because I was not confident in shaping or sharpening tool bits.

Now, thanks to some experience and the help of many on this forum, I use both carbide AND HSS. I mainly use carbide the large metal removal and then leave maybe 0.1mm or so for finishing in HSS. The 0.1mm is a generous amount but it lets me sneak up on the final dimension.

Not sure if it's the right way but I just what I do is sneak the finishing tool up to the workpiece until it ever so lightly scores the surface, I then reset the cross slide scales to zero. Any error I impose on the tool position (ie being too close to the workpiece for a zero reading) is of little consequence as I have given myself 0.1mm of wiggle room to cut, measure and adjust as necessary.

I have never tried the paper method or shim method but perhaps I may give that a go too.

Cheers

Simon

To 're-register' for a cut, I will typically leave things a little oversize and then with the new tool, take a small DOC (a thou or 2), measure and adjust accordingly. On the mill I use a bit of shim to set up cutters but the same technique could apply.

Michael

Is your oversize of .1 correct, as this seems quite small for finishing, around .25/.5 mm ( .010"/020" ) gives a lot more leeway.

Originally Posted by pipeclay

Is your oversize of .1 correct, as this seems quite small for finishing, around .25/.5 mm ( .010"/020" ) gives a lot more leeway.

Yea see what you mean. I guess I mean 0.1mm on the cross slide dial, which ultimately is 0.2mm over dimension in diameter.

Simon