Thread: Question about threading

If you have excess Springing 1 cause could be the size of your bar,as well as the depth of cut.

You would be best to use the largest diameter bar you can for the bore to give the bar more ridgidty and less spring.

If you tool is set to high above centre that will cause the tool to dig into the bore as the material is grabing the tool and pulling it into the job.where as below centre it is pushing it away.

Originally Posted by lather

rfurzer
was that 61 degrees instead of 51 ?

Damn, did the stupid 29 degree trick after the last message, had been confused due to other imfo from other sites.
no wonder it worked better previously set at 60 degrees.
the run out grooves are a great help.

now for cutting a 30mm bar, there is no way my lathe could cut 4mm off the diameter in one pass, even 2mm diameter is a struggle.
usually only cut 1 mm from the diameter each pass using the diamond tool holder.
Do you feed much slower when cutting 2mm from the diameter, find its faster on my machine, to do 2 passes of 1mm cuts, rather than a single 2mm.

the other reason i don't perform deep cuts is the worry that the tip may dig in and cause something to go flying.
Had a scary situation when boring, lucky the machine was at a low rpm, the bar somehow grabbed into the workpeice, was surprised by the amount of flex, not only of the boring bar,looked as if the post- top slide- cross slide and even the chuck were flexing. May have been an illusion- scared the crap out of me.
After that experience, finding it difficult to perform deeper cuts.

will look into getting a 28 tooth gear.

was planning on gluing 2 or 3 thou brass shimming material on the top slide and another sheet under the post to take the wear and tear. when worn easy to redo.

I have been thinking about your problems with grabbing etc and one thing that comes to mind is if your gibs are tight enough. They should be done up so their is a light to medium drag when that axis is moved. Also the tool post should not turn on it's own or need paper under it, you need to tighten it up tighter so it doesn't turn.
Your lathe should be able to to take a 2 mm DOC with a 2hp motor at lower rpm, the thing with machining is to get rid of the excess material as quick as possible to save time.

The boring bar itself probably sat too low, not the actual bit, when the bit of the HSS bar is at center height, the bar itself sits at a lower central position.
The 1/4"bit boring bar would sit half the bits width lower, this would be even lower when including the angle of the bit.
the bit would need to be ground down more than half way to get the actual bar in a central position.

the lower section of the bar was too close to the work, probably a little less than 1 mm, It was a deep bore about 60-70mm, seemed the swarf built up under the bar which caused it to dig in.
need a bar thats in between the 1/8 and 1/4 HSS boring bar size.
since that problem occured, had raised the bar more and ground down the bit, its only a worry when the diameter of the bore is a few mm larger than the bar.

Dave, perhaps they are loose, is it normal for the post and topslide to rock a little when performing broken cuts, only cut 0.125mm when machining broken cuts.
any deeper the rocking movement gets worse.

erm yes!

61 is correct 51 typo

sorry

As for the feed rate. I'd need to pop out to have a look at the actual settings but it's quite fine (appropriate for a reasonable but not superb finish when the diamond is swung round to the finishing setting). I'd guess that it was taking 15 secs to cover 60mm.

I have been working through Harold Hall's Lathe course and in the second chapter he takes us through a project to make a mini surface guage. He recommends playing about with speeds and feeds and suggests trying 2mm cuts (ie 4mm off the dia) and says that deeper cuts should be possible "if the lathe is sound" but not to bother. He shows a myford super seven which does not have the oomph of the al960.

I am not sure why your lathe isnt happy

As for digging in- less likely to happen if you are at or below centre height and the diamond should give us an element of safety too (their blurb suggests that the tool will slip in the holder in a disaster- presumably you have to be somewhat lucky)

Also - presume that you are using a tailstock centre?

O.k.
gave it a try at cutting 2mm and 4 mm from the overall diameter.
It seems to cut 2 mm o.k.
can do double this, except way too slow when feeding,
not sure what changed.
had taken the cross and topslide out about a month ago, to give them a clean before adjusting the play.

Tailstock came out of center as well, when adjusting it, the bolts were loose.
it was out by 0.08mm on a 100mm shaft. ( now its fine, 0.005mm on a 300mm shaft).

Should have tried cutting deeper after the readjustments.

the only other problem is the play of the cross slide screw, its 0.25mm,
when trying to adjust this to reduce the play it feels way too tight.
Its the main reason i dont part, as the tool may pull in 0.25 mm breaking the bit.
some sites for other lathes state to adjust this, so theres only 0.02mm play, trying this on this lathe would wear the brass nut.

When doing a deep bore usually only take small cuts, the bar definately bends down if cutting 0.5mm from the diameter with it hanging out about 60mm, , this is noticable when doing internal threads, there is too much flex.
When boring - would having it a touch above center height be safer, if the tool bends down, it wont grab due to the bores inner wall being further away from the tip.
.

There is some free play in the crossslide- I'd reckon that mine is 0.20 or so as well

I use the AXA parting tool and have had good results so far.

I am a definite newbie but tend to find that a larger boring tool set higher than centre works well. Bit tricky to work out how much cut you've put on 'tho. I got a set of 5/8 shaft cemented carbide boring tools with the AXA and am reasonably happy so far. They are not so tolerant of being run a bit on the slow side as HSS and like to have a faster speed than I would choose at first go.

(When I got the box of "boring tools" my wife said that she was at school with those blokes! )

I will have to have a closer look at my tailstock and see if an error is creeping in