Thread: Cleaning up surface of internal bores on lathe

Originally Posted by elanjacobs

You should be able to get perfectly finished bores straight off the tool with the right insert and cutting parameters. What material, speed, feed and cut depth are you using?

Sorry for the late reply. ......I use mainly alum and bronze. I don’t have quick change gears so I’m stuck with the feed rate on my lathe. If I try to run high rpm to get a clean internal finish I get a fast feed as well. If I drill or ream I get much better results. I use replaceable inserts on my boring bar Not sure what brand they are very standard looking boring bar set up ....I’ll try to radius another brazed tip boring bar and give that a whirl ......I thinking / planning of my final pass being a blunt rub rather than a fine cut. I’m pretty new at this

Lack of quick change makes it harder... uncoated CCGT inserts are the choice for ally; they have a ground and polished edge and are super sharp. They're great in bronze as well, but you'd need to get coated ones for wear resistance.

I’m totally Loving my new passion for machining metal on my lathe and mill , with all these new tools and attachments, boring heads, eBay , single point Threading , forums with helpful exprerienced people ...so much to learn. I’m starting to wonder if I have to brain space available to fit in all the new knowledge....I might have to delete 30 plus years of carpentry knowledge to free up some space in my head

If you are not changing gears to alter feed rate , the feed will be the same at 1rpm as it is at 1000rpm.

Originally Posted by STEVEMORSE

Sorry for the late reply. ......I use mainly alum and bronze. I don’t have quick change gears so I’m stuck with the feed rate on my lathe. If I try to run high rpm to get a clean internal finish I get a fast feed as well. If I drill or ream I get much better results. I use replaceable inserts on my boring bar Not sure what brand they are very standard looking boring bar set up ....I’ll try to radius another brazed tip boring bar and give that a whirl ......I thinking / planning of my final pass being a blunt rub rather than a fine cut. I’m pretty new at this

Don't use the powerfeed then... Just nice and steady on the handwheel works pretty well. Or make an adaptor to drive the handwheel with a cordless drill.

What lathe are you using anyway? There might be another way around it...

Originally Posted by STEVEMORSE

I’m totally Loving my new passion for machining metal on my lathe and mill , with all these new tools and attachments, boring heads, eBay , single point Threading , forums with helpful exprerienced people ...so much to learn. I’m starting to wonder if I have to brain space available to fit in all the new knowledge....I might have to delete 30 plus years of carpentry knowledge to free up some space in my head

No need to delete any knowledge, the unused stuff will naturally get pushed to the back as long as you don't poke too much new stuff in at once - particularly if you're starting from scratch with both a lathe and a mill !!

With aluminium - apart from the tooling side, try a bit of WD40 or kerosene as a cutting fluid and see if that helps. Just an occasional squirt - no need to drown anything.

Your insert tooling, are you using sharp uncoated inserts made for aluminium or just the typical (relatively blunt) coated ones intended for steel? The latter don't go so well on aluminium.

Don't be scared to have a crack at making your own tools either. The cheap insert tooling has its place but don't expect miracles from it.
If you're not in a hurry you can get great results with a bit of HSS in a home made holder.
I was doing some ~50mm bores about 100mm deep today and found my smaller bars were too short/flexible.
I've got a bigger bar which uses a large WNMG insert - great for removing material, but I cant get a nice finish in mild steel with it.

Made up this bar in about 20mins to take a piece of HSS. Drilled the hole for the HSS in the mill at roughly 45deg, then drilled and tapped for a 6mm grub screw to clamp it. The hole was just slightly smaller than the corner-corner dimension of the HSS blank so I touched it up with a square file until it fitted. A round hole is perfectly OK too, and the only reason I didn't just use a round hole was that I ran out of Z height on the mill for a normal length drill bit, so used an endmill to drill the hole and it wasn't quite large enough.






Steve

Originally Posted by STEVEMORSE

Sorry for the late reply. ......I use mainly alum and bronze. I don’t have quick change gears so I’m stuck with the feed rate on my lathe. If I try to run high rpm to get a clean internal finish I get a fast feed as well. If I drill or ream I get much better results. I use replaceable inserts on my boring bar Not sure what brand they are very standard looking boring bar set up ....I’ll try to radius another brazed tip boring bar and give that a whirl ......I thinking / planning of my final pass being a blunt rub rather than a fine cut. I’m pretty new at this

Hi Steve, Guys,

Don't you have any threading gears ? If so just set up for the finest possible thread. On my Myford, without the QCGB the finest thread gives me 2 thou per turn of the chuck. Using the leadscrew to drive the saddle is my finest feed amount.

My comment about finishing passes at high rpm also making my auto feed fast as well must have sounded very primitive and was definitely incorrect ....for some reason I thought my horizontal threading screw was ratio matched to the speed of my chuck and I kept that wrong info in my skull. Since opening up the box on the end of my lathe and messing with the lead screw gears I now realise the lead screw speed is completely isolated from my chuck speed , and as someone here suggested I can adjust the gears to give a very slow lead screw speed ..... so I will do that that and look at my finished surface , then I will try a radiused boring bar tip and see how that works too. I’m working with mostly bronze and ally, some steel. My inserts are general not Material specific I don’t think, As I progress I will research more about how to get hold of different Inserts, and I think I need to experiment with some HSS TOO , and practice making my own cutters , At the moment I’m geographically close to machinery house in Brisbane I’m also aware of a few other tooling supplies places in bris. And eBay of course ....thanks again to all of you for taking the time. I’m on other forums dealing with non metalwork subjects where I’m experienced and can offer as much Advice as I Can recieve, but here for a while I’m gonna be a bit of a leach, ( but a grateful one who says THANK YOU !) .... I picked up my first internal threading bar today and it’s not likely I will have the patience to wait for the weekend To give it a try so perhaps my neighbours might have some lathe noise tonight as they drift off to sleep

Steve,

Just a quick tip, if you are going to try internal threading, thread from the chuck towards the tail stock. Much better than crashing into the back of the work. Don't forget that the tip must be on centre height and the bar parallel with the lathe axis.