# Rough Finish



## pyrobrewer (Oct 15, 2013)

I am facing a large piece of mild steel flat bar that is just under maximum size for the swing of my lathe (SC4). It is a heavy but balanced and have set the speed for 400 rpm

I am getting a good finish on the outer portion of the piece but quality goes to crap toward the centre. 
I guessing the cutting rate is changing as it nears the centre and I am reluctant to increase speed as the piece is quite heavy. Any tips


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## chrsbrbnk (Oct 15, 2013)

try an oil based cutting fluid , change cutter tip radius , change cutter rake  the cutting speed goes to zero as it gets to the middle  but the feed rate remains the the same per rev, of the spindle.  check cutter center height


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## Forestgnome (Oct 18, 2013)

Looks to me like maybe the tool isn't on center. You didn't give enough info, but I'd use an HSS tool and use a finishing cut of 10-20 thousandths after sharpening the tool. You might be dulling the tool on the interrupted cuts. A lighter cut might extend the life of the tool through the duration of the cut.


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## dave-in-england (Oct 18, 2013)

Facing off common or garden Mild steel never gives a good finish, even when turned under ideal constant surface speed conditions on a CNC lathe.
The leaded EN8a variety gives a slightly better cut and finish.

The intermittent cut here on a small and not too rigid lathe, it is going to be futile trying any more.

Your best option is to take the plate to a engineering company and have it cleaned up on a surface grinder.

You will then have a smooth finish which will also be perfectly flat.

dave's  $0.2 opinion


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## jwcnc1911 (Oct 18, 2013)

as you go in, surface footage becomes "smaller" so the closer to center you need to increase rmp to match that of the outer where the finish is good.

Google "surface footage explanation" to see more


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## Arcane (Oct 18, 2013)

This might be completely off base but you might check the cutting edge of your bit, especially if it's an indexable carbide bit and check that your bit holder is locking down tight. I had a similar experience once making an almost identical cut. I was in a hurry and was taking a too heavy cut and didn't lock down the tool holder (KDK) tight enough in my haste. The bit biting into the two metal edges every revolution eventually took it's toll, chipped the cutting edge on a carbide insert and combined with a loose tool holder... well, everything went to hell in a hurry. And cheap inserts sometime seem to chip as if by magic. I don't know what setup you have so maybe this is not relevant...

Best of luck,

billy


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## Swifty (Oct 18, 2013)

As others have stated, it's all to do with the decrease in surface speed the nearer you get to the centre. Instead of cutting, the material is being ripped off leaving a rough finish. Try to make sure that your tool is sharp to promote cutting.

Paul.


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## Tin Falcon (Oct 19, 2013)

The likely causes have been mentioned several times so will not beat on that. 

This is one time where a fly cutter on a mill will do a better job than a lathe. 
IMHO having it surface ground while will solve the problem is overkill and counter intuitive the point here is home shop machining. 
I am guessing you do not have a mill or a large enough one for this piece. 
Personally I would take the item to the belt sander and smooth down the ridges.
But you may not have a belt sander with metal cutting belt. so silicon carbide paper and oil should smooth out the ridges . A little flat filing to start may speed things up.  
Tool makers and die repairmen have used files and abrasives for years to smooth and correct a lot worse. Your shop your dime you are the QC guy that needs to be made happy. 
Tin


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## goldstar31 (Oct 19, 2013)

I have to disagree with most of the comments. 
There are basically only two ways to fine finish metal apart from burnishing it and these are by cutting with a finely honed tool and secondly with a succession of abrasive materials. In professional practice both methods will be adopted.  In other words, a highly finished part will be machined almost to size and then finished on a grinder. We are a long way from that and in all probability we haven't got a grinder. What we seem to have is ill set or ill ground and finished tools- or shudder- both.

Normally, a home lathe is set to first remove excess metal and then reset to remove the last bits to size and to a high finish. That means honing the finishing tool and then setting it to rub or to shave the last few 'tenths'. 

What the expert will always repeat is that the finish reflects to finish on the cutting tool. 

I've read a great deal about this and that here and elsewhere but the tool which does the work is the one which is so sharp that it will not only pare one's finger nail but reflect the dirt in it.

If it doesn't then one has to resort to poorer expedients. 'Nuff said


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## WOB (Oct 19, 2013)

What you are witnessing is what my old college machine shop instructor call cutting below "critical speed". At the first lab class, he turned a piece of steel about 6" in dia. The rpm was set to show that the outer parts of the piece were smoothly turned and how the finish deteriorated when cutting speed dropped off as the center of the piece was reached by the tool. His suggestion was to speed up the lathe as needed to maintain cutting speed above critical as much as possible. This is less of a problem with carbide tooling but is a problematic with HSS tools due to their cutting speed limitations. 

CNC lathes are often programmed to speed up as needed to maintain surface finish. 

WOB


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## Philipintexas (Oct 19, 2013)

I've looked at your photo and read the replies and I'm still intrigued by your dilemma. I make a part of aluminum that requires a similar cut but I get no such problem. May I ask how you hold the material? is it in a 4 jaw chuck gripped at both ends and near center on the sides, or is there a protrusion on the back side at the center of rotation held in a 3-jaw? It's odd that when the cut goes bad it isn't the same across the part at a given diameter, but starts near the edges with some good results but goes bad part way across the material. Also, I assume you are cutting from outside toward the center ?  My take is there is some resonance caused by poor support of the material that allows this to happen. Does it destroy the cutting edge of your tool? I've turned lots of solid steel to the center at many different surface speeds, certainly slower than you are using,  but never saw a result like yours. 
Again, is the material solidly held near the center or does it flex away from the cutter???


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## goldstar31 (Oct 19, 2013)

Somewhere about 1955 or so, an article was written up in Model Engineer. The writer was using a 7 x 19( a Myford ML7) and was producing swarf which was what he described as 'barely perceptible' and this was far finer than the finest steel wool. 

I was writing about this condition which was made using hss tooling and ground up on a home made double ended grinder as these things were too expensive for home workers like him.

He hadn't a milling machine and his drilling machine was also home made.  There is no mystery in all this- people are still doing this on home made jigs.

That is what I am writing about.


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## rcfreak177 (Oct 19, 2013)

I totally agree with the statements in regards to surface speed being too slow towards the center.

Yes surface grinder is an option povriding you have the access to a machine or have the funds to take it to a shop.

As Tin said, fly cutting on a milling machine will give you a good even finish, providing you have access to a milling machine.

Also a carefully honed HSS tool may work as well, although with the intermittent cut this will probably dull the edge quite quickly and there is still the surface speed issue. Done correctly will leave a nice even finish though.

There is another way that comes too mind, may be a bit crude and is not the most healthy option for you'r lathe. In the past I have made a bracket which holds a 4" angle grinder in the tool post with the disk roughly parallel with the job surface and mounted a flapper disk. Then used this to act as a surface grinder as such, obviously the part will need to be rotating, generally the opposite direction to the grinder wheel. This has given great results in the past providing you only apply light cuts with a fairly slow feed and spindle speed to match.

Cleaning all excess oil from the machine to stop grinding dust sticking and setting up the lathe with newspaper or similar across the bed-ways is crucial also thorough cleaning and oiling afterwords to prevent premature wear.

Baz.


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## Swifty (Oct 19, 2013)

Philipintexas, you mention that you have no trouble finishing aluminium of this size in your lathe, but you must bear in mind that the original poster was machining mild steel. Some plate mild steel is fairly dubious when it comes to its properties and can be very hard to get a finished surface with a single point tool. On the other hand, aluminium is far more easy to machine and gentler on the tooling.

Paul.


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## Forestgnome (Oct 20, 2013)

If you all aren't getting a better finish than that facing mild steel you're doing something wrong. I know it won't be as good as grinding or flycutting, but way better than the photo.


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## goldstar31 (Oct 20, 2013)

Sorry- no!  One doesn't use a single point toil. To finish one 'rubs' the part with the side of a lathe tool-- not the tip. 

It seems that I'm not really getting anywhere here. We have got the simplest problem of the simplest tool in the workshop. On another forum a couple of us were happily prattling about removing metal. He had trained as a fitter to do one of the first jobs of an apprentice and that was to make a set of three accurate reference plates by filing, scraping and finishing with abrasives. 
I'd overhauled several machine tools and a lot of 'funny things' as well. The important thing was that we both knew how to scrape minute amounts of metal- with the slightly rounded edge  of a scraper- not the tips.

Politely, can we re-run the problem- using traditionally accepted practices?  All that a lathe or mill is doing is exactly the same as that by another generation  who did it did it  by hand.


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## Philipintexas (Oct 20, 2013)

SWIFTY: Yes, I realize alum. is different, just saying I think this is a problem of lack of rigidity in the work as opposed to the cutting speed. As I said, I've cut to the center of junk steel at slow speed and never experienced this kind of finish. 
I think the poster wants an answer to his particular problem not suggestions of different methods that might be better. 
Given what he's trying to do, I think it can be done with decent results if there is adequate rigidity in the work piece and tool.

I just did a trial cut similar to the one originally posted. 2" X 4.5" X 3/8" thick hot-rolled steel (?) in a 4-jaw chuck, light cut (.025) with a HHS tool @ 425 RPM and a slow feed, no lubricant. My results are, the finish improves toward the center of rotation.  As expected, the interrupted cut is slightly rough and finish improves when the cut is continuous even though it is painfully slow surface speed near the center.  

To address the original question, Even though it's not necessarily the best tool for his job, what caused his finish to go to pot?


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## pyrobrewer (Oct 21, 2013)

I think i'll just get a mill! Needed a good excuse  
I'm thinking Seig X2 or X3 family (liking X3) Any one had both?


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## Forestgnome (Oct 21, 2013)

pyrobrewer said:


> I think i'll just get a mill! Needed a good excuse
> I'm thinking Seig X2 or X3 family (liking X3) Any one had both?



Getting a mill doesn't fix the problem. Just like the lathe, you still need to learn how to use it. All of the same issues apply to both machines, speed, feed tool geometry, etc.


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## danstir (Oct 21, 2013)

Not having done machining that long myself I created several pieces that looked like this.  Eventually I seemed to get better by practicing sharpening my HSS tool and by getting over my fear of turning the work piece at a higher speed.  Hope this helps.


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## rcfreak177 (Oct 21, 2013)

I Have a SX3, great machine in its manual form, mine is now cnc and is even better. I have never owned or used an X2. I will not harp on about the manual X3 or SX3 as I only used it half a dozen times before the conversion.

There is another guy on this forum (rodw) Rod also bought a SX3 a while back and had some good things to say about the machine.
Here is his thread in regards to his gear.
http://www.homemodelenginemachinist.com/f15/rods-aussie-shed-19885/

 Rod is also a great guy to chat with, (lives not that far from you near Brisbane) I am sure he will rate the machine in manual form for you.

This goes without saying but having a shop with both a mill and lathe makes thing so much easier, also opens up broader horizons for potential projects.

I say if the funds are there go for it, you won't regret it.

Baz.


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## Philipintexas (Oct 21, 2013)

PYROBREWER:  Now that you have us all wondering, how did you hold the material as shown in your original post??


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## goldstar31 (Oct 21, 2013)

Experience dictates that the tool was not at correct height. There is  signs of is or  what was a pip. I would have thought that it would have instantly brought a correction of tool height. After all, that is about the only useful thing that QC tool things possess( in my opinion).

OK, I have had my say but there are others who are now writing on Madmodder about -how to grind a suitable tool- without a jig.

Not my way of doing things but seemingly a vast improvement to what has happened. Certainly worth a look.

What is also 'worth a look' is the excellent series of suggestions by a Mr John Moran in his Gadgetbuilder website.  He constructed a jig to Martin Cleeve's design-- and I made one up. Again, he describes several tool and cutter grinders and offers his opinion. Now, I have a Quorn, I have a Brookes or more correctly, the improved version as a Stent and a Kennet and a Clarkson. He describes a Tinker which is something that one makes in a easy week and out of lumps of metal. Actually I have the plans but making one is rather overkill but the principles are excellent.

Whatever your views and experience, Mr Moran has certainly provided a lot of clever machinery.


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## pyrobrewer (Oct 22, 2013)

Philipintexas said:


> PYROBREWER:  Now that you have us all wondering, how did you hold the material as shown in your original post??



This is the only photo I have of the setup as it was - 4 jaw chuck jaws gripping 2 on each long axis. There is a video that also shows nothing. I had to move the plastic safety cover over by one screw hole to avoid it tapping on the job. It was in tight as I was worried about it flinging around the room!

Am I being unduly cautious about this? 

What speed would a "pro" spin this at?

 Tool Bit was checked against centre in tailstock and passed through the centre of the job without noticeable tit. The were some regions of smooth running (in the bad section) so I checked the Tool for tightness,  post was secure as well as slide gibs all tight. Carriage was locked down using the built in carriage lock which I have found to be not very good or at least I am not very good at using it - this may be more likely. I had to fix it once as it had fallen of the tightening screw! It is just a small tab that simply grips the bottom of the bed.

However! on closer inspection with 10 power loupe a chip had broken off of the indexing tip. It was my last and am waiting for new tips from hare and forbes.

https://www.machineryhouse.com.au/L005A

Are these available somewhere separately as i will soon have an excess of threading tips!

http://www.homemodelenginemachinist.com/attachment.php?attachmentid=65282&stc=1&d=1382433783


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## goldstar31 (Oct 22, 2013)

If you are running out of tips, you should ask yourself why.

Carbide is not a very forgiving material and the least mistake of whatever sort will break the tip. 

Last evening I had 5 minutes to myself and went into the workshop  after a long absence- to see what damage from damp and see whether I had given the wrong information. I grabbed the first spare tool- a wrong chamfering tool, stuck it in my little grinder and cut a facet holding it in my fingers. All went well and then I lost the cutting edge. In my haste, I'd forgotten to tighten the tool holder down. OK, I put the edge back on the tool in seconds but this was hss. I'd lost a few minutes and at no other cost to myself. Even then the finish with a loose tool was far superior to yours. 

The moral is obvious.


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## pyrobrewer (Oct 22, 2013)

goldstar31 said:


> If you are running out of tips, you should ask yourself why.
> 
> Carbide is not a very forgiving material and the least mistake of whatever sort will break the tip.
> 
> ...



I've run out of tips because I have never bought any! The tips I had came with the machine, my first. 

I am glad you were able to produce a better result than my FIRST attempt at this procedure. 

 I am sure that I have made many schoolboy/apprentice mistakes with the 5 or 6 pieces I have chucked up so far. And no doubt will make many many more, as I am happily at the start of what I hope to be a long, steep learning curve. 

Also, as a complete newb, unfortunately you will need to explain the "obvious moral"


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## goldstar31 (Oct 22, 2013)

The moral or morals might be summarised as 
1. a correct set up
    I admitted what I did wrong.
2. then there was the question of being able to 'soldier on' regardless of being stuck for tooling. I'd chosen high speed steel bits but I could have rummaged for an old allen key or a cycle spoke or a bit of a cracked ball race- to mention three equally unusual but more than possible tools.

I must emphasise that I did refer you to tooling and techniques which were adopted by other workers- rather than myself. I was at pains not to suggest that my approach is not the only way of doing things.

I can only apologise if this has caused offence to you.


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## pyrobrewer (Oct 22, 2013)

Thanks you have given me an idea to make a flat faceplate that I can glue sheets of abrasive paper onto. You are correct about the lack of large equipment, I have a bench fully set up for Jewellery work (on of my trades) I have to get used to scale up from MM to inches 

Mill is on the wish list. 


Tin Falcon said:


> The likely causes have been mentioned several times so will not beat on that.
> 
> This is one time where a fly cutter on a mill will do a better job than a lathe.
> IMHO having it surface ground while will solve the problem is overkill and counter intuitive the point here is home shop machining.
> ...


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## pyrobrewer (Oct 22, 2013)

rcfreak177 said:


> I Have a SX3, great machine in its manual form, mine is now cnc and is even better. I have never owned or used an X2. I will not harp on about the manual X3 or SX3 as I only used it half a dozen times before the conversion.
> 
> There is another guy on this forum (rodw) Rod also bought a SX3 a while back and had some good things to say about the machine.
> Here is his thread in regards to his gear.
> ...



Cheers mate

I have done some correspondence with Stuart From Titan about mills. My initial enquiry was about http://www.ebay.com.au/itm/200976330837

I then asked about the SX3 and he suggested the TM25v
http://www.ebay.com.au/itm/200977847587 it is the same as the one listed but with a belt drive.

[ame="http://www.youtube.com/watch?v=m_T9EiLIU6U"]http://www.youtube.com/watch?v=m_T9EiLIU6U[/ame]

I just got out of hospital (gall bladder removal) and have a sympathy card to play against the financial controller, but I am not sure it will stretch double for the TM25v no matter how much better it is! Maybe I could have something else removed! And after buying the lathe she is aware of the "accessories" which can double the price again. 

Rod would be 3 1/2 hours south of me if he is in Brizzy 
Cheers
Mick


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## Tin Falcon (Oct 22, 2013)

I think the biggest lesson learned hear Is.......................
Carbide loves speed. But ........ is sensitive to shock pounding  and easily damaged by intermittent cuts. 

Usually when things go south it is because we forgot to follow the basics. 

so what are the basics ?

1) work held securely I think you did that. 
2) tool
a)   correct tool for the job would have been a good grade of HSS with cobalt.
b) held securely minimum stick out 
c) correct height  

Speed rpm of the lathe calculate based on material and diameter of the material and tool material. Use chart  or clulator such as 

http://littlemachineshop.com/Reference/CuttingSpeeds.php

feed how much the tool is avanded per revolution. 

lube coolant sulpherized oil or water suluable oil for steel 
hope this helps. 
Tin


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## pyrobrewer (Oct 22, 2013)

Tin Falcon said:


> I think the biggest lesson learned hear Is.......................
> Carbide loves speed. But ........ is sensitive to shock pounding  and easily damaged by intermittent cuts.
> 
> Usually when things go south it is because we forgot to follow the basics.
> ...



Thanks Tin 
Much better post than "mine is better than yours", or "you did it wrong" type posts
I know I did it wrong/poorly thats why I asked the question...
Cheers
PS Had a good laugh when i worked out what avanding the tool was!


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## Philjoe5 (Oct 22, 2013)

I would only add one item to Tin's list.

Every cutting operation on the lathe puts a force on the cutting edge of the tool.  Even a relatively rigid set up on our hobby lathes will result in enough force on the cutting edge to flex the tool and give a rough finish.  So what to do?  When you're near to the size you want to machine to, reduce the cut depth and you'll reduce tool flex and improve finish.  On my 350 lb lathe, a finishing cut is rarely more that 0.002" - 0.003", often less than that. 

Cheers,
Phil


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## pyrobrewer (Oct 22, 2013)

Philipintexas said:


> SWIFTY: Yes, I realize alum. is different, just saying I think this is a problem of lack of rigidity in the work as opposed to the cutting speed. As I said, I've cut to the center of junk steel at slow speed and never experienced this kind of finish.
> I think the poster wants an answer to his particular problem not suggestions of different methods that might be better.
> Given what he's trying to do, I think it can be done with decent results if there is adequate rigidity in the work piece and tool.
> 
> ...



My, what a big chuck you have! It wouldn't swing on my lathe!


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## pyrobrewer (Oct 22, 2013)

Philipintexas said:


> SWIFTY:
> I just did a trial cut similar to the one originally posted. 2" X 4.5" X 3/8" thick hot-rolled steel (?) in a 4-jaw chuck, light cut (.025) with a HHS tool @ 425 RPM and a slow feed, no lubricant. My results are, the finish improves toward the center of rotation.  As expected, the interrupted cut is slightly rough and finish improves when the cut is continuous even though it is painfully slow surface speed near the center.



I have not yet seen a tool mounted the way yours is. It must be very easy to grind that tool as it appears to have just one facet?


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## Philipintexas (Oct 23, 2013)

It's my go-to tool for almost everything. It's called a "Diamond tool holder" and comes from your country. One quarter-inch tool will last a life-time and it's easy & quick to sharpen. www.eccentricengineering.com.au


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## Forestgnome (Oct 23, 2013)

Personally I've had more problems with carbide during facing operations than any other cut. Sometimes I'll get a little flex right at the tit and off goes a chip on the carbide. I use HSS unless I'm cutting cast iron or hardened material.


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## pyrobrewer (Oct 23, 2013)

Philipintexas said:


> It's my go-to tool for almost everything. It's called a "Diamond tool holder" and comes from your country. One quarter-inch tool will last a life-time and it's easy & quick to sharpen. www.eccentricengineering.com.au



You have sold me on it (and their website) I have ordered the 9.5mm L&R option pack and an extra bit!


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## Tin Falcon (Oct 23, 2013)

The Other basic I should have mentioned if set the tool to prevent dig in. Like phil said there is a tendency for the tool /machine /setup to flex when force is applied. 
My first list mentioned steps to minimize the flex. But one must also remember to position tool in such a way as when the tool flexes it moves away from the part when more force than it likes is applied. 
So how does one do this ?
Facing think of the tool perpendicular to the part. Slightly toward you is OK but the tip away from you may case dig in. 

Turing  tool on center or slightly BELOW .
boring slightly ABOVE center. 
Tin


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## goldstar31 (Oct 24, 2013)

I appear to be getting swept up by other people's opinions. Whether they are right or wrong or argue which is better or worse but my way to tackle a long job rather than the turning in the face plate of 'my' bit of square stuff is to sweep face using the faceplate or catchplate ( or even the 4 jaw  at a push) holding the work on the saddle.

Within the limitations of something like a 918/920( I had one), I also had- probably have a gimcrack bit of round with three positions to hold a short length of hss tooling and for it to have a No2 Morse taper to hold it in the spindle. Now this is how the people who wrote the books and did all the designs that people today are making or copying or improving went about their business. It was not until about 1973 that the first real milling machines became available for the likes of them and me.

I made up a Ned Westbury mill from home made aero chocolate castings from the local college.- I know. The little sweep face effort was Martin Cleeve who never had a mill of anysort.

My contribution for today. People can argue, disagree or do whatever they deem appropriate but that is what done-- and it worked.


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