Smooth cuts??

[lazylathe]

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

 

[steamer]

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

Try that. ;D

Dave

 

[picclock]

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

 

[Jasonb]

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.

 

[Brian Rupnow]

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

 

[lazylathe]

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!

 

[steamer]

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

 

[steamer]

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/

 

[lazylathe]

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

 

[steamer]

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

 

[lazylathe]

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

 

[steamer]

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

 

[lazylathe]

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

I just have the standard one!

Andrew

Dave


PS Does you lathe look like this one?

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




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

 

[MachineTom]

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

 

[steamer]

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

 

[steamer]

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

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

Dave

 

[lazylathe]

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

 

[steamer]

Happy Burgers! ;D


Dave

 

[Brian Rupnow]

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.

 

[MachineTom]

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.