# Smooth cuts??



## lazylathe (May 14, 2011)

Hi All,

As i get closer and closer to actually building something on the Myford, i found the need to grind some HSS cutters.
I looked around the forum and used Brian Rupnows method explained here:
http://www.homemodelenginemachinist.com/index.php?topic=5569.0

The tool looks the same, i copied the angles and it looks okay.

Now when i go to cut something it leaves tiny ridges in the finish and not a smooth surface.
I have the tool set on centre and am using the slowest cutting speed on the lathe, without using the back gears.

Tried making the radius slightly bigger, but that did not help either.

Also thought it might be vibrations so i removed the 3 jaw and tried a shorted bit in the collet but no change.

Any ideas on what should be the next step??

Thanks,

Andrew


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## steamer (May 14, 2011)

Put a small radius on the tool tip... Slow your feed down and increase your speed a little bit.

Try that.  ;D

Dave


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## picclock (May 14, 2011)

Hi Andrew

It would be useful to know what material and size you are turning as some 'mystery' steels can be very difficult to get a good finish on. If the finish is poor it could be because the tool clearance angles are not correct, the gibs are loose, the tool is extending too far out from the toolholder, and a host of other things.

What speed are you turning at ? Different metals have different cutting speeds and too fast with an aggressive cut will often give a rough finish, as well as blunt the tool.

More information and pictures would make diagnoses a lot easier.

Best Regards

picclock


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## Jasonb (May 14, 2011)

What angle are you holding teh tool at, Brians grind is best used with very little clearance behind the tool like in this post

http://www.homemodelenginemachinist.com/index.php?topic=5569.msg58829#msg58829

The more you hold the tool at right angles to the lathe axis the more it will act like a threading tool

J

Steamer it dose have a rad end.


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## Brian Rupnow (May 14, 2011)

On the last few tools I have ground, I have put in no top-rake at all. This comes about as a result of having installed an AXA style Quick change toolpost on my lathe. If you have much top rake at all, then the center height of your tool changes as you sharpen it and you end up constantly having to adjust the tool height. I find that the tools cut just as well without the top rake, but you can get some issues of long stringy chips because with no top rake, you have no chip-breaker effect. I do most of my cutting at 970 RPM on stock less than 3/4" diameter, with a cut depth of .005 (radial)--(Takes .010 off the diameter) when turning steel and if I'm turning aluminum I double the cut depth and jack the speed up to 1620 RPM on the last 'finish cuts" with about a .002" radial cut depth. I don't use the lead screw to move my carriage, I do that manually. Lots of cutting oil helps.---Brian


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## lazylathe (May 14, 2011)

Okay, so i took some more cuts this time with oil and the same results.

You also have to remember that my NOOBNESS will most likely shine through on this for a lot of you!! ;D

I took 3 pictures.
The first shows the tool and it's relation to the work. A bit of ALU






The second one shows the resulting cut and the ridges i am talking about





And the last one is an overall shot to show the setup of the top slide and type of tool holder etc...





If any other pictures would help just let me know!

Thanks for all the help so far!!!!
It is really appreciated!

Andrew

PS In regards to turning speeds.
I have no idea on how to change the speed on the Myford, apart from changing the belt position or using back gears.
I have a whole pile of change gears but am unsure of how to use them to get a slower turning speed.
Just using the the as it came to me.
The Myford manual is not much help when it comes to reducing the speed.
I did change the 1/4hp motor for a better 1/2hp one, so could that be the problem?
I can always change it back to the original one!


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## steamer (May 14, 2011)

It appears that you feed rate is too high.  I think your going to need to slow down the lead screw a bit. ie I think it needs to be geared down to run slower, so you will need to change the gearing at the headstock end.

I assume that the Myford has a gear chart...probably inside the gear cover.

If you trace which gear is where, you can determine with the chart what feed rate you have.

It is usually listed as to how many thousanths of an inch per revolution of the spindle.

The tool marks I see look like it is set very high right now.  Check it out

Jason, that's what it looks like to me. The finish seems fine, it just needs a lower feed rate.

Hope that helps.

Dave


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## steamer (May 14, 2011)

Hey Andrew,

Take a picture of the gear chart and the lathe at the headstock end.  We can help out better if we can see the controls.

No worries mate....we can lick this.

Dave


PS Does you lathe look like this one?

http://www.lathes.co.uk/myfordml7photoessay/


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## lazylathe (May 14, 2011)

Dave


PS Does you lathe look like this one?

http://www.lathes.co.uk/myfordml7photoessay/


[/quote]

YES!! Minus a few of the nice goodies....
I will post a pic of the gear chart and gearing as it is now!!

Thanks Dave!!!

Andrew


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## steamer (May 14, 2011)

OK.

The WHITE numbers with the BLACK background are the screw pitch attainable

The WHITE numbers with the RED background are the feed rates attainable.


To switch between the two you need to swap the gear position shown on page 2 of this document, position "A"  With it one way you can cut threads, with it the other way you control your feed.

http://www.pilotltd.net/s7gbox2.pdf

Arrange things for about .003" lead for your cut and give it a go.  It should be much better.

What you have now is a thread with a thread form that is part of a circle.  What you need to do is make the pitch of this thread much smaller...and the "thread" will go away.

....Well...at least that's what "I" think it is anyway....I'll get proven right or wrong soon enough. ;D

Dave


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## lazylathe (May 14, 2011)

Mine does not have red background... See the pics.
No Gearbox on my lathe...

Okay, so here are the latest set of pictures.
I just included the Imperial chart, which does not make a lot of sense to me...
I like the Metric one!










I also included a picture of the gears as they are set up.
I marked the number of teeth on the two main gears that i could clearly see the numbers on.





Hope this helps!
I have been looking at the gearing chart but thought it was just for cutting gears....

It was quite nice to not read " What the H**L did you do to the cutter!" So that was pretty nice! ;D

Andrew


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## steamer (May 14, 2011)

Ahh OK, no quick change.

Try this doc instead

http://www.metalwebnews.com/manuals/myford-super7lathe.pdf


Arrange your gears for about .0037"/revolution....as seen on your gear chart...down near the bottom.

There should be a stud gear set that gets swapped for threading/turning.....I have'nt read thru it yet...but I know you can ;D

Dave


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## lazylathe (May 14, 2011)

LOL!!!
When i said minus a few goodies...
Minus:
gearbox
clutch
fancy pulley

I just have the standard one!

Andrew




			
				lazylathe  said:
			
		

> Dave
> 
> 
> PS Does you lathe look like this one?
> ...


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## MachineTom (May 14, 2011)

I don't know if you have an S-7 or an ML-7. Inside the gear cover should be a chart like this.






this is the feed and threading chart to install the change gears needed to cut specific threads and feeds. The photo is the top of the chart but you will use the bottom portion for your feeds use a feed of .0058 as a general start.

The definitions of the terms used in the chart are: Gearing from spindle to leadscrew. The numbers denote the number of teeth each gear has. all gears are stamped with teeth count.

TPI- threads per inch, Feed per Rev- how far the carriage moves with each single turn of the spindle.

Driver-This is the first gear that can be changed, it is the outside gear of the group of gears on the forward/reverse lever, its the only one that is held on with a small BA screw.

1st Stud-This is the compound gears, 2 gears on a common keyed shaft, driven is the gear that engages the gear before the first compound set, Driver the gear which drives the gear after it. Thinking from spindle to leadscrew.

2nd stud_- Same

Idler-An idler is a single gear that spans or connects to other gears

Lead Screw_ the gear on the end of the leadscrew

As you lay out the gears you think from spindle, but when you assemble them they are installed from leadscrew towards the spindle.

So to get a carriage feed of .0058" per rev

Chart





You would need a 20 as driver, a 55-25 first stud, a 60-20 2nd stud and a 65 on the leadscrew.

Clear as the Mississippi,... Right


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## steamer (May 14, 2011)

Oh...and the cutter looks fine....no worries there...if it wasn't it would have chattered.

Actually, it looks really good and the finish is nice....its just that it's in thread form at the moment..... ;D


That should clean up nice once the feed rate is dropped down.

Dave


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## steamer (May 14, 2011)

YUP  .0058" / rev will probably work too....

Pick what's ever easier, as the lead right now is just too high.

Dave


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## lazylathe (May 14, 2011)

Thanks guys!
I also found this site:
http://www.duncanamps.com/metal/software.php

It is an ML7, wish it was the super 7... :

I will read through everyones posts a bit later!
The wife is shouting that i need to BBQ the burgers or else... ;D

Andrew


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## steamer (May 14, 2011)

Happy Burgers! ;D


Dave


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## Brian Rupnow (May 14, 2011)

I agree totally with Steamer---To fast a feed rate. I don't know Myford lathes. Does the Myford allow you to turn the leadscrew manually to take a cut? If so, try that, feeding the tool slowly---The "screw thread" should disapear.


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## MachineTom (May 14, 2011)

It took me so long to put together the post you already have the chart, but I'll continue along.

You need to slow down what you have, The problem is its is generally not quick with change gears to do this. A look at your setup shows a quick possible of changing the gears driving stud 1 and driven stud 2, with a smaller gear on 1 and a larger gear on 2. Count the teeth on those studs and add them together, 60+~40 guessing that it will be about 100, look in your pile of gears for two gears that added together equal that number exactly, if so they will swap with changing anything else, if not then strip off all the gears and put together a set that will give you the feed you need.

The gear sets are supported by a cast iron bracket called a quadrant, often refered to as a banjo, due to its appearance. This bracket is bolted to the lathe with bolts stuck behind the leadscrew gear, and you will find out that sometimes you can't access the bottom bolt with the leadscrew gear on, but you need to have the leadscrew gear on to set the backlash, catch 22. So what you do is after stripping off the gears, loosen the quadrant bolts, move the quadrant down and snug one bolt(the easy one) assemble each gear set and set the backlash, a postit note run between the teeth is just right, after all the gears are installed, remove the leadscrew gear, which usually means removing the 2nd stud gear as well, loosen the quadrant bolts and set backlash between first stud gear and drive gear, tighten the bolts and reinstall the 2nd stud and leadscrew gears.


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## steamer (May 14, 2011)

" postit note run between the teeth is just right, "


I agree with everything you said Machine Tom....especially the post it note!

I use writing paper some times too.

Dave


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## lazylathe (May 14, 2011)

Thank you all so much for the info!!!

I will work on this tomorrow morning and post my results!

I had a feeling it was too fast but lacked the instruction and knowledge to safely do what needed to be done!

Thanks for showing me the right way!

Will post pics tomorrow!!

Andrew


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## Lakc (May 14, 2011)

MachineTom  said:
			
		

> a postit note run between the teeth is just right,


What a marvelous idea for the cheap no brand postit notes we have at work. :bow:
What other practical uses are there for sticky notes that dont stick?


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## Maryak (May 15, 2011)

Andrew,

The leadscrews on a lathe are always cutting a thread, maybe not of recognised size pitch etc., but a thread none the less. The idea is to overcome this by:-

1. Using the change gears to make this thread as fine as possible.

2. Grinding your tool so that the cutting surface is greater in size than the pitch of whatever thread your change wheels are set at, meaning it removes the ridges and leaves a smooth surface.

Sometimes it is possible to have a heavy rate of feed, (leadscrew advance), combined with a wide cutting face on the tool and a very light depth of cut and still have a good finish. It is a technique I was taught when machining steel pump shafts. The time saved was astronomical with these 6ft long x 2" dia. shafts.

There are some well proven relationships between speed in ft/min of rotation and speed in feet/min of leadscrew advance and depth of cut, for most of the common metals such as iron, steel, brass, bronze, copper and aluminium which should, if all else is OK, give a reasonable finish to the surface being machined. Most of these figures are for commercial rigid machine tools, for our hobby machines 9 times out of 10, IMHO halving these figures will give reasonable results.

The other important thing is lubrication and cooling which again depends on the metal being machined.

Hope this helps

Best Regards
Bob


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## steamer (May 15, 2011)

As Bob has rightly stated, there is a "right" feed and speed for every metal.  Most are published in the "Machinery Handbook".  This I should have stated.  At the time, I thought that understanding the lathe was a bit more pressing.  Andrew, once you get through this, get ye a Machinery handbook. A Used copy is fine as this data has only changed since carbide tooling became prevelent. Most of my machining is with HSS, and therefore at a lower feed and speed rate......lots to learn ;D


Dave


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## websterz (May 15, 2011)

Lakc  said:
			
		

> What a marvelous idea for the cheap no brand postit notes we have at work. :bow:
> What other practical uses are there for sticky notes that dont stick?



Tiny little paper airplanes? :big:


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## lazylathe (May 15, 2011)

KARMA all around for those that helped!!!! ;D
You guys are awesome!!!!!! :bow: :big: :bow:

I had to go down to 0.0043 to get a nice smooth cut that looks almost polished!!
Will post pics later tonight, i have a model engineers meeting to go to soon!

Thanks for all your help and the pictures posted!!!
It made it so much easier!!!
And now i know one more "trick" to get a smooth finish!!!

Thanks again!!!
Pics up later.

Andrew


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## steamer (May 15, 2011)

Cool!

Dave


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## Brian Rupnow (May 15, 2011)

So---did you change the feed rate or just take a lighter cut?


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## lazylathe (May 15, 2011)

Brian - Lighter cuts made no difference.

I changed the gears and reduced the leadscrew rate to 0.0043" and that made a huge improvement!
Attached is a picture of before and after.
Closest to the chuck is what i was getting and the end section is where i am at now.
I think i can live with it like it is!
A quick go with some compound, fine water paper or polish will really make it shine.

The pic is just after a cut with oil.
Same tool as the last pictures.






Thanks again for all the help and guidance!!
It was really appreciated!

Andrew


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## steamer (May 15, 2011)

Hi Andrew,

Glad everything is coming around!  Also glad you learned something.....

A couple more observations.....call it the grad class if you like

I wouldn't extend the work much more with out some support from the tailstock in the form of a center.

I think the old rule of thumb is 5:1 (length to diameter)....I'm sure I don't remember it right...and I'll be corrected.

If I was to want a polished turned surface, start by making sure you have a polished cutting tool. If you look under a magnifying glass, you will amazed at how rough a tool looks after it comes off the grinder. All those striations get transferred into the work. Spend some time with a couple of slip stones and bring the cutting edge right up to mirror. You will be amazed at how nice a finish you can get, and how much sharper the tool is! It also means that you will cut with less cutting force....which is always a good thing on any lathe but especially on small lathes...

Keep the over hang of the tool to the absolute minimum. Especially with a round nose tool, but with any tool really.  It's stiffness decreases with the cube of the length. and the tool will become a tuning fork in a real hurry!...so choke up on that tool.

Glad your having fun and making chips...keep at it, its very rewarding!

Dave


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## lazylathe (May 16, 2011)

Thanks Dave!

That length of material is about 5 inches long.
The other side was center drilled when i first started this adventure and was supported by a live center.
I only turned about a 3/4 inch length outside the chuck and then extended it so that everyone could see the
change in cut.

I am still a bit wary of my first "big" lathe.... :-\
So it just gets used on the lowest speed which seems pretty fast to me! 

Now i just need to figure out how to get out of doing yard work... ;D

Andrew


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## Troutsqueezer (May 16, 2011)

lazylathe  said:
			
		

> Now i just need to figure out how to get out of doing yard work... ;D
> 
> Andrew



Now you're just being silly. That's impossible. 

Ouch! Stop that, Honey! I'll be out there in a minute......I just want to finish typing this........ :big:


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## lazylathe (May 16, 2011)

Ouch! Stop that, Honey! I'll be out there in a minute......I just want to finish typing this........ :big:
[/quote]

I see we are all in the same boat here.... ;D
Oh well we will use whatever free time we can get!!!

Andrew


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## Ned Ludd (May 18, 2011)

Hi Andrew,
Out of curiosity, where did you get the advice to have your top slide at such a strange angle? Most people would suggest it is at right angles to the cross slide, although some recommend 3 or 6 degrees, to get a very fine in-feed. Others suggest you move the top slide around to 30ish degree, or half thread angle, to the cross slide (not lathe axis) for threading purposes, but this is completely unnecessary for successful threading and I don't suppose you are screw cutting yet
Ned


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## steamer (May 18, 2011)

The compound doesn't look so bad...though I'd argue to straighten out the toolpost making it square and parallel....

Dave


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