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View Full Version : Mini Lathes, part 2



Dunc
03-15-2008, 09:48 PM
I posted a query about some aspects of the mini metal lathes. Thanks to all who responded with some good pointers.

Neighbor is certainly interested but he has some questions that I can't answer (no experience with a mini). His questions suggest that I ask for more forum assistance.

1. Compared to a "real"/regular/standard lathe (with comparable specs like a 7-8 " nominal capacity and not compared to a 14-16") that uses a fractional horsepower induction motor vs the direct drive on the minis... can a mini take a decent cut (turning to diameter or facing operations) in mild steel without bogging down? Space is a consideration and he has no need of the longer bed capacity.We realize that the speed will initially drop under load but it should pick up as the electronics compensate. This is sort of a backing-in way, I guess, to ask what kind of torque is available? He's prepared to accept that the machines aren't capable of hogging a lot of material per cut but he wants to know that it can do some "real" work. Not trying to offend anyone with this line of questions but genuinely want to know. For meeting expectations is a mini a standard 7" lathe but with a short bed? Or... ?

2. While the 4-jaw chuck (independent) question was asked and answered - thanks to everyone - is it possible to use a collet chuck? Make/model? Plans to adapt the Taig collet or?

3. Is milling with this lathe feasible? Thinking stress, strain and setup rigidity? If yes, how? Up to what size of milling cutter? Milling adapter and vise: Taig or another make/model?

4. Are these minis capable of using a drill chuck & twist drills (1/2")? Not thinking of power to do the job but is there enough space along the bed or would short-shank drills be needed?

5. Can knurling be performed? Would use one of the scissors type (knurl wheels at top & bottom of work rather than the toolpost type that exerts pressure from the side.

Once again, thanks to all who read and answer this post.

DancingBear
03-15-2008, 11:27 PM
Dunc,
I am actually on my second mini-lathe, I originally had a 7x10 and now have a 7x14. I've been using them for about seven years now.

I've been known to take 0.040 depth cuts in mild steel, i.e. removing 0.080 diameter. The times I've tried more the machine made discouraging sounds. Down to 60-80 RPM torque seems OK, it drops off after that. The electronics do seem to regulate it pretty well.

Before I got a mill I had a milling contraption for the 7x10 consisting of an angle plate, the lathe compound, shims to deal with the raised section of the compound slide, a plate to bolt the vise on, and a small screwless vise. It worked on aluminum, but I never tried milling steel. Littlemachineshop.com sells a milling attachment, but I haven't tried it.

Jobber length drills (i.e. normal ones) can be cumbersome to use on the short bed, I finally bought a set of screw machine length drills and found they were much handier to use.

Yes, knurling is possible. I never liked knurling steel with the toolpost type of knurler as it seemed like it put a lot of pressure on the headstock bearings. I finally bought a scissors knurler recently. I really like it, but I haven't had to knurl anything tough since I got it, so I can't report about that.

Hope that helps.

Walt

pcarpenter
03-15-2008, 11:39 PM
I have bigger machines now, but have thus far hung on to my mini-lathe and mini-mill. In answer to the cut depth issue as well as the knurling issue: Most of my work was in aluminum with the little lathe. I only knurled a couple of pieces and because I just never wanted to put wear on the spindle bearings, I bought a cheap scissors tool and used it. It worked fine in both steel and aluminum.

I found that the motor is not so much the limiting factor in cutting depth, especially with good sharp HSS tooling. Really, I think you will exceed the rigidity of the compound before you would trip the motor protection. Because it is such a high speed motor, you will do most all of your work in low range...which gives quite a bit of torque. Rigidity of the lathe overall is high due to its short form factor. Its short and stout. Its a neat machine within its work envelope.

I think I have drilled to 1/2" in the past--and I only own standard length drills. The limits depend on the length of the work. The size of the drill chuck will make a difference too. I went with a 5/8 chuck which probably wasted some length. Edit-- I do have the Grizzly 7x14 however.

Its a good machine for small work. People who don't own them complain about making improvements to import machines, but I got satisfaction out of the work. I made an apron gear cover, shortened the compound plinth to allow an AXA toolpost to be fitted, made a tailstock cam-lock, milled the cross slide for extra travel, and made an extended cross-slide bearing housing.

Paul

GadgetBuilder
03-16-2008, 12:05 AM
1) Ability to remove material is really dependent on power. I generally cut 25-40 thou in steel but can cut 100 thou with lower feed rate. I suspect cubic inches per minute is the same. Many users favor the low speed range but I use the high speed range about half the time.

2) Lots of options for collet chucks, search this site:
http://www.littlemachineshop.com/ LMS is a good reference for parts and tooling needed for the minilathe. Because there are so many in use the tooling options available are considerable.

3) Milling is shaky and not really satisfactory, although I did it initially. Convinced me to get a mill :D

4) Drilling up to about 3/8 hasn't been a problem on my 7x12 in most cases - perhaps I just work on shorter items. I've drilled to 1" using S&D drills. These large drills often chatter although they work fine when used in a 10" Rockwell. The tailstock doesn't seem as solid as the rest of the machine.

5) Bump knurlers can be too much for the machine, depending on work size and material. I built a clamp knurler - using only the 7x12 (before I got a mill) and this works fine on the 7x12.

John

JRouche
03-16-2008, 12:21 AM
Hmm.. Difficult to answer really..

Depth of cut... I only take more of a cut for time reasons. Meaning, if I am gonna have to remove a lot of metal. Say starting with a two inch round block of steel and I want to turn down part of it to one inch, say for a shaft of a fly cutter project. That will take some time on the 7x... lathes. But if time is not a deal they can do it.

Thats the funny part. A guy with a lil 7x lathe can do it. They can produce some outstanding parts on the lil lathe.

But its nice to be able to take the DOC a lil more, just to get through the tedious part of removing metal..

I have a South Bend 10L and its large steps beyond what the 7x lathe can eat, but I am still running into power limitations. I will bog the motor down to its capability and want for more power.

There always jobs that you will be limited on power. Even if you have a largish lathe. I have a buddy with a shop and a pretty large Reed Prentice 25" lathe.. I have even been around when he has almost stalled the spindle, a 25 hp spindle, just cause he is pushing it to the limits.. Oh, on a separate thought thats when I gained an appreciation for carbide bits!! He drove the bit to what I thought would be complete failure but the 25hp gave up first!!!!

Sorry, I digress... You can accomplish many jobs on the 7x lathes, its just gonna take longer.. You want to remove metal faster you are gonna need more power..

So, can you beef up the 7xx lathe with more power? Sure.. You can put a 5hp motor on it. Will it tear the lathe up, yup..

Oh, and I would like to see a forty thou cut in steel with the 7XX lathe.. I can chew out .100" with the SB, alot more with the monarch but I had a really nice cumins 7XX and I couldt get close to .040 (.080 total) at any speed. Just a thought..

And, if the foot print of the lathe is critical, say in a condo garage, which I was in. And cash isnt too big an issue I love the lil speed lathes folks like hardinge put out. You can adapt an x-y table to them and talk about power for a small lathe.. Plenty!!! JR

Fasttrack
03-16-2008, 12:49 AM
If you are concerned about taking big DOC or having enough power, get a bigger one! I think having a mini-lathe or smallish lathe is great for those small precision parts but if you ever think you will need to turn a 2" shaft to 1", do yourself a favor and start looking for a larger lathe. You'd be surprised what you can fit in tight places.

I'm not saying this to insult any mini-machines. Everyone who has them seems to like them but having run my smithy for a long time, it really sucks when it takes you 3 hours to make a simple jackshaft. I thought i was just a newb and didn't know how it was done correctly. Turns out, when done correctly, you take off a big bite and get it done in no time flat. Working on a 13" harrison (still only moderately sized) and i can take off .1 and not think i'm destroying the machine. You talk about taking .05 off and it takes you a long time to get anywhere!

So, imo, they are terrific for small precision parts. Bad for larger parts (precision or otherwise)

Ideally, we would all have a small mini lathe, a moderate sized lathe (Sheldon?), a high-precision tool-room lathe (10EE) and a monster lathe (hmm 20" HD pacemaker?), just to cover all possible needs :D Well thats just me anyway...

Yankee1
03-16-2008, 01:00 AM
Hi Dunc,
I would advise anyone buying a small 7x12 to purchase a insert type tool holder such as "www.plastools.com" makes. Most carbide type tools are negative rake and require more power to use. The tool holder sold by Plastools is built specifically for small lathes and works very well. I have one and I really like it. It uses the least expensive insert and has six cutting edges. It uses the TNMG-222 and cut far better than the other carbide tools available which are negative rake. Take a look at their website. There is a lot of great information on it.
Chuck

JRouche
03-16-2008, 02:08 AM
Hi Dunc,
I would advise anyone buying a small 7x12 to purchase a insert type tool holder such as "www.plastools.com" makes. Most carbide type tools are negative rake and require more power to use. The tool holder sold by Plastools is built specifically for small lathes and works very well. I have one and I really like it. It uses the least expensive insert and has six cutting edges. It uses the TNMG-222 and cut far better than the other carbide tools available which are negative rake. Take a look at their website. There is a lot of great information on it.
Chuck


Really good info, for sure.. But for the small 7xx lathes I think HSS bits are perfect. You can grind a huge amount of positive rake which works well with these small lathes,

The tnXX type inserts are still negative rake and even with the tool holder counter acting that with a positive pocket you are still dealing with a pretty blunt edge of the insert. I like the cost factor of being able to grind your own bit and tip for the small HP lathes using HSS. And you become proficient with grinding the angles and have flexibility..

And dont get me wrong. I use nutthin but inserts, positive rake though. And they are pretty cheap if you look. I have tried to use the neg. inserts and on the smaller lathes the geometry of the neg. inserts still need some power to curl up the chip., even when tipped over with the pos. type holder.. As common as the pos. inserts are I sugest using them. You do lose the flip side of them for cutting but I dont imagine in a home shop it matters much.

The deal is with the tool bit holders. Thats really where the investment is. Pick a few tool holders that you will use and make sure the inserts are available for it, for cheap. JR

loose nut
03-16-2008, 11:51 AM
You have to take into account the type of material you are cutting, 4140, free machining etc. Everything changes with different types of metal. As a rule of thumb I was always told .050" DOC per available horse power on steel thats not to tough, less for tougher materials, how much HP does a 7" lathe have, take it from there. The harder you strain the lathe the shorter it's life will be.

GadgetBuilder
03-16-2008, 01:00 PM
Per Tubal Cain, a lathe can remove 1.5 cubic inches per minute per HP at the chuck in mild steel. So DOC depends on material, HP, work diameter, and feed rate.

The 7x12 was the only lathe I had for over 4 years. Out of the box I certainly couldn't achieve the DOC I mentioned above. But eventually (a couple years, I learn slow) I found what made my particular 7x12 work well. This included some "tuning" of the machine, learning that the machine was sensitive to where the slides were positioned as far as overhang of the tool from cross slide and that tool geometry is very critical in a low HP machine. My conclusions differ from some others in this thread -- I found that carbide didn't work well with my 7x12 as described here: http://www.gadgetbuilder.com/MyShop.html#Carbide

I did find that a tangential toolholder with its steep rake works exceptionally well on the 7x12 -- the steep rake increases the effective sharpness of the tool so it removes material with less effort. Given this clue, I found that a knife tool (using a chip breaker to increase rake) will also take deep cuts. Neither of these techniques change the maximum amount of material per second that can be removed with the 7x12's limited horsepower, they just let me get closer to that maximum.

The 7x12 is somewhat limber in the slides so steep rake tooling allows it to take deeper cuts because it reduces the force on the cutter (and thus the tendency to chatter); this doesn't change the material removed per second. Also, deep cuts don't work out on large diameter work. A DOC of 40 thou is reasonable in mild steel on work diameters of 1" or less and I'd be happy to demonstrate this to JRouche or anyone else who has had difficulty achieving this on their 7x12.


I also found that the tangential when moving from left to right produces a much better finish than moving right to left. The slicing action works well but limits the DOC. This lead to using a vertical shear tool when finish is important.

Bottom line is I think my 7x12 works well but it took me a while to understand what the machine was trying to teach me. What I learned from the 7x12 seems to translate well to the slightly larger 10" machine that has joined it in my shop.

John

jdunmyer
03-16-2008, 01:43 PM
I have a 7X10 lathe in addition to a 19" LeBlond, and use the little one a lot.

Scissors knurler works well.
I use only HSS bits, mounted in a QCTP from LMS. I have about 4 extra toolholders. Parting tool uses a 1/16" bit.
4-jaw chuck came from J&L, IIRC.
Mods to lathe were made per the several web sites devoted to it.
No need for a cam-lock tailstock: buy a 17mm combination wrench at a flea market and cut it in half. The box end will hang on the clamp nut and works just like a camlock lever.
Regular drillbits work OK, and you can easily drill up to 1/2"
Torque limitations only affect me when I'm trying to thread something with a tailstock die holder. About 1/4-20 is pushing it, but 5-40 works great.
I seldom push the DOC above .020", but it'll do more.

Larry Swearingen
03-17-2008, 10:35 AM
I've got a Grizzly version of the 7x12 with a LMS QC toolpost.
I find that the most DOC I can get without too much chatter
is 40 thou on 1" diam more or less in Mild steel. If you want to
feel good about your lathe get some 12L14 ! {:>)
Cast iron machines easily too if the diameter is small enough.
I recently made a 6" faceplate for the lathe out of some 6"+
cast iron from Enco. I had to use a pretty fine DOC to keep
from stalling the motor at 6" diameter. The compound is also
a little flimsy. The spec that they use for travel of the compound
is WAY optimistic. Given much overhang at all and it's chatter city.

I used a milling attachment on the lathe 1 time. I took the compound
off and bolted the attachment directly to the cross slide. That was to mill
a 1/4" keyway in a shaft that I turned down to get my Rockwell mill working.
It got the job done but wasn't what I would call pleasurable work.
Wanna buy a milling attachment ? :">

I find the biggest PITA in the 7x family is that they use only
1 set of ways shared by the Headstock, Carriage and Tailstock.
So you are limited in working close to the tailstock to setting
the cutting tool on the right side of the toolpost or angling it
to the left a lot.If you choose to angle it that means that you
are severely limited in how close you can get to the chuck on the
headstock end. Should have sprung for the extra to get a 9x20.
Wait. The 9x20 is a belt change machine and I'd lose the variable
speed motor that I like so well.

All that said it does what it was probably meant to do and I
probably wouldn't have gotten a lathe if this hadn't been available
at the price it was. So I'm grateful for that. Those $400 South Bends
aren't easily found. And when they are it's usually another $400
shipping.

Larry S