Author Topic: I hate these mini lathes....  (Read 13775 times)

Offline kiwi

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I hate these mini lathes....
« on: June 06, 2010, 04:37:56 PM »
Hi..
Do you guys with these mini lathes "7x14" have a prob
keeping it adjusted...I seem to be retightening the jibs
every few weeks....
Was turning a guide  the other day useing the live centre
& it just kept chattering....found to tail stock was out of
alinement.."AGAIN"..this thing is really starting to pee me off..

I need a bigger lathe.. I think I give this poor little thing a hard time..

Any way heres a few tips/tricks to quickly check a few things..
setting tool hight & centre alinement....I think the pics exsplaine them selfs !

Pete
Kiwi

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Offline arbantelope

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Re: I hate these mini lathes....
« Reply #1 on: June 06, 2010, 07:45:46 PM »


Kiwi. No offense. But I did'nt understand a word you just said, nor do I have a clue as to what you are trying to show in the pictures. lol I'm joking around - but dead serious about my lack of lathering knowledge. I'm sure the rest of the gang will know exactly what they are looking at. Is it cold? Maybe start with a good warm coat for it - may help with that chattering.

Alan - NorCal

Offline daved

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Re: I hate these mini lathes....
« Reply #2 on: June 07, 2010, 03:54:36 AM »
Actually, he was demonstrating some very good ways to verify that you have your cutting tools properly centered.  I'd heard of this particular trick, but had never seen it demonstrated in such a simple and graphic way.  Thanks, Kiwi, you just made my life a lot simpler :-)!

As to the chattering, I'm afraid it's just the nature of the beast, the only fix is to ease up on your cuts or get a bigger machine.  One of the main reasons I ruled out a 7X mini lathe almost immediately.  Later.

Dave

Offline MartinDWhite

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Re: I hate these mini lathes....
« Reply #3 on: June 07, 2010, 03:58:55 AM »
I did a bunch (A BUNCH) of looking and talking before I bought a lathe (which has still to arrive) and the advise I saw over and over was buy BIG. The little (7X and 8X) lathes are toys or for tinkering with. I suggest you sell that one and get a bigger one. Keep in mind this is currently arm chair advise since my lathe won't arrive for a few weeks still.

   Martin D. White

Offline RCnMo

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Re: I hate these mini lathes....
« Reply #4 on: June 07, 2010, 08:18:16 AM »
I've found that sharp HSS tooling works better on my mini lathe. It keeps me from tending to hog out pieces (overworking the machine). I save the carbide for my big lathe. BTW, I like the ball in the chuck idea. I use a dti on a test bar.
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Offline TCups

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Re: I hate these mini lathes....
« Reply #5 on: June 07, 2010, 10:52:35 AM »
If the tailstock (pointed cone) were aligned precisely with the ball bearing in the center of the lathe's chuck, then the flat plate clamped between the two would be perpendicular to the axis of rotation, not angled off to one side.  If the bar stock in the chuck of the lathe were turning concentrically with the tail stock, then the cutting tool positioned to the side of the bar stock would remain centered on the OD of the bar stock instead of appearing to drift up and down, again causing a plate positioned between the tool and bar stock to tilt inward and then outward as the chuck is turned, I believe.  So, when the workpiece rotates, the cutting tool only "bites" on a partial arc of the rotation, causing the lathe to chatter.  Correct?

Offline Truman

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RE: I hate these mini lathes....
« Reply #6 on: June 07, 2010, 12:24:40 PM »
Chatter can be caused by many factors! Tool support is one. Seat the tool as close to the tool post as possible. Correct spindle speed and cutting speeds for the material is critical for a good finish! If you cut too slow, you create excess heat that can work harden the surface, blunt the tools and even set up a harmonic frequency in the material that shows itself as chatter. Too fast can also create the same problems! Loose Head stock bearings will also show up as chatter. Tool height is important but is not as critical as tool rigidity from tip of tool to the bed of the machine! When I say tool height is not as critical, it is important but if the tool is a few thou low, it will only change the geometry of the tip by a small amount! Preferably, it should be on C/L. Another thing to check on is the state of the jaws in the chuck. If the jaws are gripping only at the back of the chuck because they are badly worn, this can show up as chatter also!

Anyway, enough of my ramblings!
cuiusvis hominis est errare, nullius nisi insipientis in errore perseverare.

Offline shady816

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Re: I hate these mini lathes....
« Reply #7 on: June 07, 2010, 01:14:13 PM »
YES thanks for the deminstration that will help me alot.

Offline fisherdude

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Great tips for adjusting mini lathe
« Reply #8 on: June 07, 2010, 05:29:15 PM »
I love my mini lathe - Cummings tool brand. I know its not as wonderful as the larger models, but it costs a lot less and it still does a lot.  The alignment tips are great!

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Offline redtank

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Re: I hate these mini lathes....
« Reply #9 on: June 15, 2010, 02:54:26 PM »
Everyone hit the nail on the head regarding chatter and size of lathe. Ive been running lathes professionally since '78 working in both tool rooms and screw machine shops, and the most important thing is to use sharp tools, a dull tool with ruin your day. Cutting above center will cause all sorts of trouble without being aware until you get near center and your cutter rides up over the top and breaks. Unless you have to weld your work piece, stay away from C1018 bar because you cannot get a good finish no matter what. I prefer 12L14 screw machine stock and can be bought in small pieces on eBay. Leaded stock cuts much easier than non leaded. If you're machining aluminum, stay with 6061T6, if brass, go with a free machine alloy. High speed tool steel with 8% cobalt will hold up well as long as kept sharp. Most carbides don't work well with carbon steels, except micro-grain types, but carbide takes more pressure to cut and gives poorer finishes. I've done okay by honing a fine edge on carbide inserts using a diamond wheel and lubricant, but only for production runs machining abrasive materials like 11L37 and stressproof. Unless you've got a lot of horsepower and fine power feeds, cut off blades can be difficult to use with out chatter. I'm surprised people are able to turn mild steel in these small lathes, I figured with the low hp, aluminum, brass and plastic are all they will cut. For a few extra bucks, I'd go with a 12" x 24" series lathe minimum. You'll get a good rpm range, enough weight to stay put, and hopefully 220v motor. A nicely tooled lathe of this size will set you back $3,200.
Cris
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Offline shady816

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Re: I hate these mini lathes....
« Reply #10 on: June 15, 2010, 03:27:30 PM »
hello redtank I am new to the lathe and machining bit and only have 6 months with my 9x20 lathe and appreciate the nice input and keep it coming.

Offline redtank

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Re: I hate these mini lathes....
« Reply #11 on: June 15, 2010, 05:10:49 PM »
Shady,
What sort of work are you doing with your 9x20? There are many tool posts out there ranging in design and age. Years ago I used to run an old South Bend with belt drive and it had a back gear. We turned and polished a lot of draw dies for the metal stamping industry. The lathe had an older style tool bit holder that would slip if you tried to take too heavy a cut. When we bored, we would mount a home made steel boring bar holder that sat up on the cross slide. Work on that lathe was slow and tedious. The belt would slip, your tool would dig into the work piece and possible yank it out of the chuck!
I prefer the dove tail type holders (quick change) that you can slide tools in and out of and simply cam lock them into position. One you have your tools set slightly below center, you can make quick work of a job. I like to have one 1/2 or 5/8 indexable hold with triangle inserts (coated), two different boring bars with indexable bits, one 3/8 and one 3/4 or 1" for ridge boring, and last, a HSS cut off blade, 3/32 or 1/8". If you can afford it, buy a digital read out (DRO) and enjoy super precision cutting!  I've done some milling work on lathes, but you need creative set ups. It's best to buy a small mill and be done with it. Now we're talking $$ but the truth of the matter is more machining work in a shop is done on a mill.
Cris
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Offline shady816

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Re: I hate these mini lathes....
« Reply #12 on: June 15, 2010, 05:41:06 PM »
redtank ...i have the quick change tool post you speak of and all the tooling  i have are the insert type and mostly i have been turning muzzle breaks and finishing barrel crowns and even threaded a few barrels for recievers and i bought a mill three weeks ago and i'm still playing with that. rookie i am.

Offline LongIslandArcher

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Re: I hate these mini lathes....
« Reply #13 on: June 15, 2010, 06:32:46 PM »
Yeah, i have one of "these" mini-lathes - a 7x12 to be exact.  The first time I ran it, the speed control module fried and now I'm waiting on Harbor Freight Tools to get me a replacement module.  It's now only one speed - 2500 rpm.  I need a parting blade.  Any idea where I can order one?

Offline kiwi

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Re: I hate these mini lathes....
« Reply #14 on: June 15, 2010, 11:43:24 PM »
hi...
parting blade & holder for the mini lathe..
plus everything ealse you will need for the mini lathe..
http://www.littlemachineshop.com    http://lmscnc.com

Pete
Kiwi

Spring guide sets...  http://www.trademe.co.nz/Members/Listings.aspx?
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If guns are outlawed ONLY outlaws will have guns

A tin of Gamo pellets is like a box of chocs U never know what yer going to get.....