AL-320 G Help

[Kpar]

I've had this Lathe for some time and have enjoyed making a few trinkets to get some machining practice. I've always had some difficulty in parting off and I'm now up to my 3rd tip holding blade and is getting a bit frustrating.
Done a lot of reading up and have followed these tips from others
1. Tool height set correctly
2. Blade parallel with chuck face
3. Speed set as per stock size.
I usually brake the blades on old axle steel. This morning i machined up a 30mm x 150mm center to hold in the chuck and broke another blade.
What I noticed just before the blade broke some shudder was experienced & the nut that holds the cross feed handle had backed off a little. Maybe this was the shudder. Trouble is if I tighten the nut very tight it seems to bind up the cross feed.
Sorry about the long thread but can somebody help me out with some suggestions. Parting off is getting expensive (back to the hacksaw)

Kpar

 

[Cogsy]

I have a similar issue with the same nut coming loose during operation of my H&F lathe (bit smaller than yours though) but it shouldn't be able to happen while parting off if you don't stop feeding in the compound. So I'm wondering if you're stopping the cut when you're parting off, or maybe just not feeding fast enough? What sort of speeds are you parting off at? It's possible your speed isn't high enough either.

Parting off is certainly not my favourite thing to do but with a sharp tool set exactly on centre and parallel to the chuck, somewhere near the correct rpm of the workpiece and constant feed on the compound, I generally don't have too many issues. For aluminium I always use some dabs of WD40 during the cut but for all other materials I part off dry. It can be a scary procedure on some parts but I've never broken a blade (runs off to knock on wood...).

 

[Kpar]

Thanks Cogsy,
you may be correct in a couple of points, yes I do take it a bit too steady with the feed, especially with old axle steel and with 30 mm dia I run about 250rpm is this too slow ?.
I guess the cross feed nut could back off when I back off with the feed. Maybe I should get some HSS blades & practice before using the insert type.
I'll try a nylon nut on the cross feed shaft and see how that goes.
Kpar

 

[Cogsy]

I'm not sure about your speed. I know it's too slow for brass or ali but it might be ok for steel. To be honest, I normally part off at whatever speed I'm turning at (because I'm too lazy to change belts just for a parting operation) and that is set by feel rather than charts. For that size steel I would probably be turning at around 600 RPM, maybe even the next step up at around 850 RPM but don't read anything into my speeds. I have no idea about 'proper' feeds and speeds and I just use what seems (or feels) right at the time. Chances are I'm way off the recommended settings.

 

[XD351]

Hi Kpar ,
Just for clarity i went out and disassembled the handle and dial on my AL 320 and when i tightened the nut up tight there was a little more drag but it didn't lock up .
I think you may have an issue with the dial binding against the cross feed housing , maybe the thrust bearing is sitting a little deep in the housing or the outer dial is a little thick .
Take the nut off then the handle and the dial assembly then take a look at the thrust bearing it should sit a little proud of the housing , mine feels about 5 thou but if you wish i can measure it for you - If it is not proud of the housing fit a shim behind it.
Next look at the dial assembly the centre hub should sit flush or a few thou proud of the outer ring and if it is not then lap the outer ring on a flat surface and use some emery paper 250 grit will do .
I recently had the exact same issue with my lathe and buying new insert holders especially from H&F made the experience even more painful !
Next thing to check is the cross feed nut retaining screw to see if it has come loose , it is in the middle of the cross slide next to the button oilers and finally for the cross slide check the gibs on the cross and compound slides and make sure they are snug but not binding .
Lastly check your head bearings by mounting a dial indicator on the saddle and set the dial up so it is reading up on the top of the chuck . Then lay a piece of timber across the bed under the chuck and use a pry bar to lightly lever up under the chuck and look to see if the dial indicator shows any movement , don't hang off the end of the pry bar too much as you may induce some flex in the spindle and there should be no movement on the dial .
I also have an AL50G and until i fitted a rear tool post i just about cried every time i had to pert anything off ! I don't think the improvement has as much to do with the so call push up and away theory as much as it does with the fact that that the rear post is solid steel and eliminates the flex of the flimsy compound slide assembly - i would suspect that a solid front tool mount would give similar results and if you don't use the compound slide often then the improvement in rigidity is well worth the few minutes to change over to the compound when needed .
My next mod to the 320 is to fit a cut down myford cross slide to the top of the 320 cross slide so i have some t slots to mount a rear tool post .
I nearly forgot to ask are you locking the carriage ?
Edit:
If the nut keeps coming loose drill and tap on one of the flats for an M3 grub screw or use some removable loctite .

 

[Kpar]

Thanks for your input XD351, Yes I had another go at the cross slide and I believe there is a binding of the dial it is binding on the housing. I've checked all potential movements with the compound, spindle bearings and yes i do lock the carriage when parting off heavy metals.
I've still got a lot to learn and any help from this forum is much appreciated.
I have no problems parting softer metals Brass/Alum/mild steel, just Stainless or 1930's Ford steel.
Kpar

 

[rodw]

I usually brake the blades on old axle steel.

Seriously, there is your problem. It has nothing to do with your lathe. I have the AL320G and parting is never an issue But I do confess having a go at 65mm dia stainless was a disaster!

You see, axles are tempered and hardened after they are machined. Get yourself some nice 12L14 or 1045 mild steel and see the difference.

At work, we have a bead roller that rolls a bead on engine induction piping that was made by Jong, a qualified machinist in the business next door. Now I was sick of borrowing this tool, so I asked him to make one for me. He refused to point blank becasue he had machined it out of axle steel as he knew we used it for rolling beads on stainless steel tubes. He had bought special carbide tips and even then broke quite a few and therefore refused to make one for me.

So the long and the short of it, while old axles are round and cheap (maybe even free), they have no place in a lathe, much less being parted off!

 

[Philipintexas]

Another tip, keep your cut as close to the chuck as possible. Use lube, and of course, don't power feed.

 

[purpleknif]

After 30+ years as a machinist I have found that the absolutely most important thing when using a cut-off tool is clearance on the tool itself. The straight high speed tools will work just fine if you tweak them a little by grinding some back clearance and side clearance . I also put a small hook, or chipbreaker on mine.

 

[Kpar]

Thanks everybody, especially rodw it makes me feel a lot better that it's not the machine but the material. I'm from the old school & my Dad always told me if i wanted to make something tough and to last, use old axle steel.
I do still have an issue with the cross feed nut always backing off. The same as cogsy mentioned. I'll address that problem & steer clear of axle steel.
And thanks XD351, I do have a problem with getting too much pre-load on the bearings when tightening up the nut.
This is fun learning.
Kpar

 

[rodw]

Use lube, and of course, don't power feed.

I disagree with this statement, I always use power feed with carbide tooling and coolant. There are other threads on this forum by more experienced than I which detail why. but the long and the short of it is that it works and the tooling is designed that way. Its maybe not axle steel, but the AL320G will part off aluminium under power feed at 1600 RPM quite happily. It is a remarkably sturdy lathe in my view.

 

[XD351]

I disagree with this statement, I always use power feed with carbide tooling and coolant. There are other threads on this forum by more experienced than I which detail why. but the long and the short of it is that it works and the tooling is designed that way. Its maybe not axle steel, but the AL320G will part off aluminium under power feed at 1600 RPM quite happily. It is a remarkably sturdy lathe in my view.

Be careful with the power feed on an AL 320 as the cross feed and carriage feed are the same crappy little lever that has a very poor ball bearing detent type locating system and if you have to shut off powered cross feed quickly it is very easy to drop the lever into the carriage feed position - a disaster usually results , don't ask how i know this !
If you must power feed on an AL320 use the lever that reverses the lead screw as it has a better neutral position and the worst you can do is reverse the lead screw which will only back the tool out or if you are power feeding the carriage it will only stop or reverse the carriage back over where you have already machined .
This of course is for turning , facing and parting as the lever for engaging the half nuts for thread cutting is a different lever so when thread cutting the lead screw reverse lever should never be used as the indexing of the lead screw in relation to the chuck will be lost .

Recently i made some hubs for a go kart out of some 150 mm bar stock , possibly i thought 4140 but i can't remember as i bought it a few years ago off Ebay and originally meant for flywheels so i didn't care what it was as long as it was for the right price !
Cost me a WNMG insert , a TCMT insert and both ends of the insert tool blade as this stuff was as tuff as although granted the inserts were only cheap crap but man it chewed them up !
Last week i was making a valve spring compressor for a junior dragster and used some rolled channel we use on the garbage trucks at work , stupid me didn't think about what this stuff was , I ended up a blunting a couple of drills and chipping a carbide drill as it turns out it was some type of work hardening alloy steel .
Sometimes free stuff can really bite you i tell you !

Ian.