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What am i doing wrong

Making a tapered cone

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duncan webster11/03/2020 14:25:41
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'ordinary mild steel' would be EN3 in my experience, as others have said it's machinable, but you get a better surface finish on EN1, which is more correctly 230M07

Martin Kyte11/03/2020 15:00:34
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Definitely agree with setting up the topslide properly. Take the slide right off and clean the ways etc. Lubricate well including the lead screw and the mating faces of on the front and rear of the leadscrew bracket. Reassmble without the leadscrew and adjust the gib by feel as you slide the topslide back and forwards by hand. You neen silky smooth with no rock. Push it fully forward and refit the leadscrew.

This bit will sound daft, by have you tried starting the cut at the bottom of the bore? I've not tried it on an internal taper but I always seem to get a better finish on an external taper when using the topslide. I have no idea why.

regards Martin

Martin Kyte11/03/2020 15:29:01
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OK so I thought about this reverse cutting thing a bit. Most tools, including boring tools have an included angle less than 90 degrees to enable turning and facing in the case of a turning tool and the production of flat bottomed holes for boring bars. In the case of boring tools the front of the tool generating the chip leads with the corner and if the cutt is deeper than the tip radius the chip will have a tendency to be forced into the cut. When turning the opposite way the flank of the tool leads and the cutting face forms a greater than 90 degree angle with the bore. The chip is therefor 'peeled away from the bore and cannot interfere with the cut. My concept is thus that when hand feeding in the conventional direction the chip generates 'stutters and wobbles' due to tiny dig in's. In the reverse direction the chip gets thrown out of the way and has less effect on the stability of the cut.

I may be completely off in the wrong direction but it sound plausable.

regards Martin

Andrew Johnston11/03/2020 15:36:16
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Posted by Martin Kyte on 11/03/2020 15:29:01:

OK so I thought about this reverse cutting thing a bit.

Don't know the answer, but I'd agree that one generally gets a better finish on the way out, for internal bores at least. I haven't tried it on external tapers.

Andrew

Martin Kyte11/03/2020 16:23:34
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Certainly the geometry that George Thomas proposed as best for boring bars had a front angle greater than 90 to the bore behind the tip. I suspect that this is one of those instances where the design of inserts gives the most utility for modern industrial machines where the problem doesn't appear with their auto or CNC feeds and huge rigidity.

We on the other hand sometime have to fall back on older methodologies.

regards Martin

Steviegtr11/03/2020 19:24:01
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Wow . You have all given me plenty to think about. Ketan, thank you for the info on the boring bars, Mine is flat on the top & round at the bottom to locate in the 250-102 holder. I will include a picture showing shape & part No. Neil sorry. I have gone & cut the end of the bar off to work on, that had the writing on it. Sure it said EN1A. The guy said it was the best for machining, he had others. The stainless I machine is 316. Not had a problem with that. Sounds like I need to change the tip & run much faster.

Also I may have been misleading with my 1st post. I was turning a 6 degree taper to make a cone for ring making. I offset the compound to achieve this. Yes the stick out was 3" , which I needed.

The other thing said was the cross slide & compound chatter. I did lock the cross slide so it could not move & I recently stripped & adjusted it, There is no chatter in that. The compound was a little loose & I could rock it slightly if I gave it a hard twisting motion. So I nipped the gib screws on 2 of the 4. It seemed to do the trick, although made it a bit stiff to turn, Hence my aching fingers.

Strangely as someone said I could get a better finish when backing out of the work. I thought this was maybe because in the way in you are removing metal & on the way out it is taking a much shallower cut.

Anyway I have read through all that has been said & will take it all in & try again, I do have a slightly smaller one to make so will see. Busy tomorrow picking up the dismantled 370Kg milling machine. So may have a back ache too. Regards.

Steve.boring bar part no.jpgboring bar close up.jpg

Edited By Steviegtr on 11/03/2020 19:27:28

Steviegtr11/03/2020 19:31:21
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Posted by SillyOldDuffer on 11/03/2020 09:32:05:
Posted by Steviegtr on 11/03/2020 01:06:00:

...

Also just a mention the steel was marked up EN1. I bought from a guy at Rufforth who sells nothing but bar stock. I have spoke to him at length so I do trust him. Ex Coded welder. So he knows his metals.

Steve.

EN1 is 'ordinary' mild-steel of the type I warned about. It doesn't machine particularly well. (Nor is it avoid at all costs horrible.)

EN1A is markedly better on a lathe because it's formulated for machinability. The specification includes the magic words 'free-cutting', and it's roughly twice as machinable as EN1.

Best of all in the family of mild-steels is EN1A-Pb. It contains Lead, and is about 50% more machinable than EN1A.

Machinability isn't an obvious concept, but the techniques needed to cut anything vary tremendously. At a pinch a wood-saw can cut butter, but don't use it on steel. Likewise Lathes and Milling machines don't cut all metals equally well, or at all! Try turning a square file into a round spike.

Beware who you take advice from, including me. A Coded Welder will certainly know about metals, but his focus is welding not machining. Different skill set. For example, a Welder should avoid EN1A and EN1A-Pb because they don't weld well! Your colleague may be completely trustworthy in the ordinary sense, but this is engineering. It's fact based, look it up in a book, confirm by experiment knowledge. Judgement calls influenced by a firm-handshake, old-school tie, convincing patter, or solid friendship aren't a good way of making workshop decisions.

Other way round when dealing with people because most of us are an emotional mess! Then personal trust matters big time.

Dave

 

Sorry it did says EN1A. My mistake. Dave the other thing you mentioned about trusting people. The reason I said it was because the guy's mum & dad ran the steel stock business for many years , He helped out when he could. Sadly on the way home from the Newark autojumble some time ago, his dad had a heart attack & passed away. His mum gave up on the business , so he took over. The company is called Blenco metals, of Doncaster. I spent an age talking to him because I worked for many years on Oil refineries. It seems he has worked as a welder at all the plants I had worked at. Anyway I digress, but he does seem to know his steel, from helping his Dad over the years. 

Steve.

 

 

 

 

 

 

Edited By Steviegtr on 11/03/2020 19:44:12

Mick B111/03/2020 21:02:42
1728 forum posts
91 photos
Posted by Steviegtr on 11/03/2020 19:24:01:

....

Strangely as someone said I could get a better finish when backing out of the work. I thought this was maybe because in the way in you are removing metal & on the way out it is taking a much shallower cut.

...

Steve.

Edited By Steviegtr on 11/03/2020 19:27:28

Sometimes I've wondered if that effect is due to the workpiece (and tool, if it's a boring bar) being in tension from the cutting force rather than compression. That might tend to damp out vibration and chatter rather than amplify it.

Maybe.... laugh

Edited By Mick B1 on 11/03/2020 21:04:07

Steviegtr11/03/2020 21:15:37
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You could be right. I did try a 10 thou cut from inner to out & it was hard going. The 10 thou cuts is what I did the cone with, I think some have said even less is better. Definitely need to design & make a neat little attachment for the handwheel on the compound. I know a lot use a battery drill.

Steve.

duncan webster11/03/2020 21:48:42
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I don't understand why a flexible boring bar would cut a tapered hole. There might be some bell mouthing as the cut comes on. But once the cut is established, and the bar has deflected by whatever it wants, then the cutting process is stable and the diameter of the work won't change. The diameter might not be what you expect, but it won't be tapered. That's definitely my experience. It's counter-intuitive but the best way to kill chatter when boring is increase the depth of cut and/or the feedrate. The boring bar may deflect a little more, but if the cutting process is stable then the bar will not chatter.

Andrew

Unless the workpiece itself is deflecting I agree, and on a boring operation the workpiece will be a lot stiffer than the boring bar. I'd also point out that the stiffness is governed only by the shape (diameter) and overhang, as long as it is steel the young's modulus won't change by using a 'better' grade. The seating of the insert in the recess at the end is a different matter, I can easily believe that Sumitomo bars support the tip better and stop it moving about on its seating, also present it at the correct angle

Steviegtr11/03/2020 23:00:07
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Posted by duncan webster on 11/03/2020 21:48:42:

I don't understand why a flexible boring bar would cut a tapered hole. There might be some bell mouthing as the cut comes on. But once the cut is established, and the bar has deflected by whatever it wants, then the cutting process is stable and the diameter of the work won't change. The diameter might not be what you expect, but it won't be tapered. That's definitely my experience. It's counter-intuitive but the best way to kill chatter when boring is increase the depth of cut and/or the feedrate. The boring bar may deflect a little more, but if the cutting process is stable then the bar will not chatter.

Andrew

Unless the workpiece itself is deflecting I agree, and on a boring operation the workpiece will be a lot stiffer than the boring bar. I'd also point out that the stiffness is governed only by the shape (diameter) and overhang, as long as it is steel the young's modulus won't change by using a 'better' grade. The seating of the insert in the recess at the end is a different matter, I can easily believe that Sumitomo bars support the tip better and stop it moving about on its seating, also present it at the correct angle

SORRY guys it was not cutting at an angle . I set it to cut a taper at 6 degree's. That was not the problem. The problem was a poor finish to the cut. The Arc boring bars do look very good & much more so than the one I have.

Steve.

 

Edited By Steviegtr on 11/03/2020 23:01:05

Andrew Johnston12/03/2020 08:32:37
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Posted by Steviegtr on 11/03/2020 23:00:07:

SORRY guys it was not cutting at an angle . I set it to cut a taper at 6 degree's. That was not the problem. The problem was a poor finish to the cut.

Errr, we'd worked that out. Despite what you might think we're not complete numpties. We're talking about a different sort of tapering, as raised by Ketan. I doubt you're problem is due to the borinmg bar, more likely to be the insert and technique.

A helpful sequence for use on forums is read, understand, post. smile

Andrew

Danny M2Z12/03/2020 08:50:01
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Maybe a lick with a toolpost mounted grindiing tool could smoothe things out a bit smiley

thaiguzzi12/03/2020 13:22:27
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1. Boring bar as big as fits in the hole.

2. Two hands or digits on the top slide hand wheel. Lock everything else down.

3. I prefer sharp HSS on anything inc internal tapered bores if i want a super finish.

4. Stating the bleedin' obvious - yes, on centre with the cutting edge every time.

Along with all of the above, and a smooth, well oiled, no slop movement on said top slide, i can get perfectly workable, wonderful finishes on 2MT internal tapers on a 51 year old Boxford.

Regards

TG.

SillyOldDuffer12/03/2020 14:54:37
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Posted by Steviegtr on 11/03/2020 19:31:21:
Posted by SillyOldDuffer on 11/03/2020 09:32:05:
Posted by Steviegtr on 11/03/2020 01:06:00:

...

Also just a mention the steel was marked up EN1. I bought from a guy at Rufforth who sells nothing but bar stock. I have spoke to him at length so I do trust him. Ex Coded welder. So he knows his metals.

Steve.

EN1 is 'ordinary' mild-steel of the type I warned about. ...

...

Dave

Sorry it did says EN1A. My mistake...

Steve.

...

OMG, my mistake, not yours Steve. Just got back to this thread to discover I blundered yesterday. Although EN1 was buzzing loudly between my ears, I was actually thinking about EN3. Wires crossed completely, hence my embarrassing essay. Possibly due to old-age, more likely carelessness!

Andrew's comment about the advisability of reading and understanding posts is all too pertinent. In my case, I clearly ought to make certain I understand my own posts.

Sorry, sack cloth and ashes for me. Again...

embarrassed

Dave

Tim Stevens13/03/2020 17:27:15
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1268 forum posts

A quick note about the ruler test for height of a cutting edge: The test will only give accurate results if the bar in the chuck is running true. If the chuck is worn (like they all are) this is not usually going to be the case, so to be sure, turn a small amount off the surface of the bar in the chuck so the ruler rests against bright new metal.

Cheers, Tim

Edited By Tim Stevens on 13/03/2020 17:28:03

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