Mini Lathe Chatter

[keys]

I'm trying to turn down 4 inch 6061 to 3.1 inches on a 7x12 mini lathe. The first problem is getting the tool back far enough to even make the cut. To do this I set the compound at 31 degrees according to the protractor on the machine. Is this the correct way to get the tool back far enough?

The other problem is some serious chatter. I have tried the following.

I have tried adjusting the gibs and carriage to the point that it is hard to move anything.

I have checked that my tool is on center.

I have tried two different tools. One a brazed carbide and the other a rounded HSS tool. Both of these tools made good face cuts and turned smaller diameter material just fine.

Swapped my A2Z quick change for the stock tool holder.


I should also mention that work piece is about 2 inches long held buy a 5 inch 4 jaw chuck. I was going to use the tail stock for support but was unable to because the tail stock comes in contact compound.

The only way I have been able to cut without chatter so far is with the carbide tool, taking 5 thou at a time, and running pretty sow (~200-300) rpm. I took a pic of my setup. I'll try and post that when I get to work tomorrow. Thanks in advance.

Dustin

 

[Blogwitch]

Dustin,

What you have to realise is the name of your lathe.

Even though it will fit into the chuck, it doesn't mean it will cut it well. Even on a largish lathe such as mine, 4" diameter is a large bit to swing about.

Look at your setup. The largish chuck is hanging on the end of a very thin spindle, then you most probably have 3" of material sticking out of the chuck, so maybe 5" to 6" hanging on that scrawny spindle. No wonder it wants to chatter.

All you can hopefully do is set things up as it looks like you already have, ensuring your tooling is razor sharp, perfectly on centre and your gibs as tight as they can get without binding. In fact. lock the gib strips on the axis that isn't going to be moving. Also have as little overhang on the tooltip as possible, it is the lack of rigidity that is causing all your problems.

Reduce your speed down to below 100 if possible, take fine cuts with plenty of lube. The larger the part, the slower you need to go, so set aside maybe an hour to take that much material off, don't expect to do it in a couple of minutes. The big boys can, we can't with our limited machinery.

We are now going to get people spouting up that they easily cut 7" material on their mini lathe, but you can guarantee they had to do a special setup to achieve it.

With any job that is getting towards the max limits of the machine, it isn't just a matter of throwing the part on and machining it. We all suffer the same problems sometimes, even us with largish machinery. There is no instant cure, it is a matter of doing the best you can with what you have available.

Bogs

 

[websterz]

If you must use the compound (and on the 7x lathes removing it is a great way to make the machine MUCH more rigid!) then you need to lock it down tight. I slip a small aluminum block up underneath the compound and crank the handle in to jam the compound up against the block. It helps stiffen things up. Ideally you want a block with a groove in it that allows you to straddle the feed screw so that the clamping pressure isn't all on one side of the screw. That can cause unwanted twist. Me personally...I just work without the compound. :big:

 

[keys]

Bogs,

You post actually makes me feel better about the situation. If I'm up against the limits of the machine, I'm ok with that. I was getting frustrated thinking I have something set up wrong, but couldn't figure it out. I knew I wouldn't get away with using 7 inch material on this lathe, but I never though 4 inch would be considered close to the machine's limits. I guess my first clue should have been turning the compound around just to get the tool back far enough. *club*



websterz,

I might have to make tool post adapter for use without the compound. That sounds like a good idea to remove some play.

Do you place the block underneath the compound between the feed handle and the piece of metal with the protractor on it? I might have to try this was well.

Here are a couple pics so people can see how I have the part setup. Bogs is right, I've got a lot of metal hanging off that little spindle. A 5 inch chuck looks ridiculous on a mini lathe.

 

[black85vette]

......on the 7x lathes removing it is a great way to make the machine MUCH more rigid! Me personally...I just work without the compound. :big:

I agree. When my 7x10 was my only lathe I made a square block out of aluminum to replace the compound. If you are careful you can make it the right height to mount the stock tool post for use with the indexable tip cutting tools. This gives you a lot of flexibility on mounting your cutting tool and frees up some space for the tail stock. As mentioned by websterz it also makes your setup more rigid.

 

[compressor man]

Dont want to highjack this post or anything but....

I have seen many people claim to get good results by removing the compound from their minilathe. I would like to do this but I would no longer be able to face something, at least by using my own self-taught (probably wrong) method. To face something I first lock the carriage down so it cannot move then I use the cross slide to cut across the face of the workpiece. I then advance my cutter by using the compound and then take my next cut.

Without a compound how can you face something? If I tried to use my carriage to advance the tool it seems that it would just wander around as I was facing ???

 

[Cedge]

Try using the tail stock and a live center. It adds a bit of stability and will often cut chatter significantly. you might want to consider the mod that increases cross slide travel if you intend to cut larger pieces. I've successfully turned 6 inch stock in my 7 x 14 Micromark after this mod was made.

Steve

 

[black85vette]

I have seen many people claim to get good results by removing the compound from their minilathe. I would like to do this but I would no longer be able to face something, at least by using my own self-taught (probably wrong) method. To face something I first lock the carriage down so it cannot move then I use the cross slide to cut across the face of the workpiece. I then advance my cutter by using the compound and then take my next cut.

Without a compound how can you face something? If I tried to use my carriage to advance the tool it seems that it would just wander around as I was facing ???

Your observations are valid. Here is how I worked around that.

Rather than locking the carriage I stop the lead screw from turning and then engage the half nut on the carriage. This will hold the carriage while you make the facing cut with the cross slide. Then manually turn the lead screw with your hand to advance the carriage and make the next cut.

Works well and you can move the carriage any time you want by disengaging the half nut.

 

[Huntinguy]

Dont want to highjack this post or anything but....

Without a compound how can you face something? If I tried to use my carriage to advance the tool it seems that it would just wander around as I was facing ???

Well, you can do it that way... I usually run my compound in until it binds against the back of the compound, In short I jam lock it. On my lathe there is a carriage lock nut just to the right of the cross slide... I lock my carriage.... Never had a problem with anything move as long as my tool was sharp. You really don't need a compound unless you are cutting tapers or threads... but hey... they look cool and lathes are supposed to have them.

As to the original post... I think you are asking a lot out of those spindle bearings....... The distance from the head stock bearing and the diameter of the part compared to the distance between bearings.... low spindle speed and light cuts....