Questions about mounting milling cutters in the lathe

[Sleazey]

I've been learning to use my lathe via Harold Hall's fine tutorial book, from the Workshop Practice Series, "#34 Lathework A Complete Course".

I am at the point I need to do some light milling work for the first project. I don't have a mill yet, and it will be a while before I do.

My lathe is a Proxxon PD 400, with an MT-3 spindle taper. The spindle bore is 0.807"/20.5mm. Tailstock is MT-2. The motor is 550 watts/0.8 hp. Swing is 6.69"/170mm. Distance between centers is 15.75"/400mm. It's quite a nice little lathe, very precise (more precise than me, that's for sure).

What is the best way to mount a milling cutter in the lathe? I have heard of people just using the 3 jaw chuck, but my understanding is that this is not a good choice; the cutter is too likely to walk itself out of the chuck due to the side loads. Is that correct?

What would be the preferred(correct) way to mount milling cutters on this machine?

As I said, this is for "light" milling work; 1018 steel, light cuts, small items.

Appreciate any and all advice!

Thanks.

 

[Speedy]

I just got my lathe days ago, so im still extremely a nub.

I am going to say a Collet holder is the way to go.

 

[gmac]

Sleazey;

Like you I have no mill. I purchased Workshop Practice Series #5 "Milling Operations in the Lathe" by Tubal Cain and found it well worth the price.

When mounting cutters in the chuck they caution about the condition of the chuck jaws and effects of vibration loosening the cutter and it moving in or out of the chuck jaws. Four jaw independent chucks provide more clamping force - the three jaw self centering chuck may be over strained clamping the cutter.

A drawbar is recommended if mounting the cutter in a Morse Taper style holder. You could probably buy some blank MT-3 arbors and drill/ream for your endmills, etc. as well as drill/thread for a drawbar.

Garry

 

[Stan]

Import MT-3 collets are almost as cheap as MT-3 blank arbors and already come threaded 3/8-16 for a piece of all thread rod as a drawbar. You can get most of the smaller endmills in 3/8" shank so you would only need one or two collets. The endmill directly in a collet in the spindle keeps everything as short as possible.

 

[Sleazey]

OK, so I need:

• 1) An MT-3 collet holder, with 3/8"-16 female thread on one end, the end that gets inserted into the spindle. The other end is for the collet with the cutting tool.
• 2) 2 or 3 collets in small sizes to hold the shanks of the endmills, fly cutters, etc. that I will be using.
  
• 3) A 3/8"-16 threaded drawbar to screw into the collet holder, thru the spindle bore. What is the length I need? I am assuming it just needs to be long enough to stick out of the spindle bore enough so that I can get a wrench onto it to "draw" the collet and milling tool tightly into the bore, and also enough sticking out to whack it with a soft headed hammer to free up the collet and tool when I am finished. On my lathe, there is about 8" from chuck mounting plate to outer end of spindle bore, so I figure I need at least 9 or 10 inches of drawbar in total. Can your drawbar be too long?

Does one leave the drawbar in the spindle while actually milling? I assume so. This would argue against having a drawbar that is too long. This would mean having the drawbar spinning with the spindle, and supported only at the collet end. That doesn't sound good to me.

Or does the drawbar get removed once it has drawn in the collet holder, and is reinserted when it is time to remove the collet? If so, is there still a danger of the collet holder and cutting tool coming loose from the spindle?

Is that all correct?

 

[ozzie46]

Sleazy

On my 7x lathe a bushing goes in the tail end of the spindle that the draw bar goes thru
and the draw bar tightens up against the bushing. If the bushing weren't there the draw bar would have nothing to tighten up against. The draw bar has to stay in or the collet will work loose. I made my own draw bar. Just 3/8-16 bolt from Lowes and I machined the bushing up on the lathe.

Ron

 

[stevehuckss396]

Good morning Sleazey!

I did not see where it mentioned what lathe you have. If you have an el-cheapo 9 X 20 asian lathe like Harbor freight Ect, then it is a MT-3. If that is not what you have, look in the manual for your lathe to see what taper is in your spindle.

What worked for me was to go to the hardware store and get a cheap 3/8-16 X 8 inch bolt and run a die over the threads to clean them up. I also made a washer that is 1/2 inch thick. It has a 1 inch od for a 1/4 inch and a .780 OD step, 1/4 inch thick. This washer fits into the spindle and keeps the bolt centered at the other end.
You don't have to do this part but i under cut the od of the bolt next to the head and made the ID of the washer about .001 smaller than the bolt OD. The washer was pressed onto the bolt. When the washer got to the under cut part of the bolt, it freed up and now the washer is captured ont the bolt. This way it wont get lost.

Picture 1 shows the screw in the collet. When the screw is tightened, the collet is pulled into the tapered bore, forcing it closed. As it closes, it grips the tool or piece of stock and must stay tight during machining. When finished, loosen the blot about 4 turns and tap the bolt head with a hammer to "pop" the collet out of the tapered bore. Then back the bolt out all the way and remove the collet.

Picture 2 shows the washer and the under cut bolt.

Picture 3 shows the washer inserted in the spindle

Picture 4 shows the collet. The hole in the collet should match the OD of the cutter and have a 3/8-16 thread on the other end.

 

[Stan]

Forget the collet holder. You have a MT-3 spindle so put the MT-3 collet directly in the spindle and pulled in by the drawbar as explained by others. Since you have to put a washer, collar or bushing in the left end of the spindle, the drawbar is supported while in use since it is pulled up tight.

The length of the drawbar for your lathe will be the 8" spindle length minus the length of the collet plus the depth of thread in the collet and space for a nut. Drawbars are a pretty simple concept and if it is too long it doesn't matter although you don't want three feet of 3/8 rod flailing around.

Endmills from 1/8" to 3/8" are readily available in 3/8" shank. Bigger than 3/8" usually the shank is the same size as the endmill. In your case you are limited to 3/4" as the max size of MT-3 collets. You definitely need a 3/8" collet plus whatever sizes you want to use above that (1/2", 5/8", 3/4" ?).

 

[Sleazey]

Thanks Steve and Stan!
You l have answered all my questions; the pics were especially helpful in clearing things up.

My work is all metric so I'll be looking for collets for metric sized cutters.

Thanks again guys; most helpful to this newbie

 

[Kermit]

Although I didn't ask any of these questions, I found the answers very helpful. I just got a new 'toy' and needed to know all of these facts.

2 1/2 inch version from enco because they were cheaper and I had a free shipping code. Have a few end mills coming as well and I'm looking for MT-3 collets now too. ;D Thanks for the learning.

What region of the great town of Houston do you hail from Sleazy?

Kermit

 

[Sleazey]

I live out in Alief, or West Houston. 4.5 miles from my job, which I bicycle to sometimes, when the weather isn't death-dealingly hot.

 

[Kermit]

I'm in old NW Houston; inside 290 and beltway 8. Same side of town and still plenty of miles between us. ;D

Nice to have a member here near me, although I'm useless as a source of learning metalworking arts. I am never-the-less open to learning anything you might have picked up

Kermit

 

[Sleazey]

Yes I had noticed before that you were in Houston too.

I am slowly learning a little bit at a time, as I try to setup my shop and my tooling, a little bit at a time.

My biggest obstacle is self imposed: I am trying to be strictly metric. I have been unpleasantly surprised at the difficulty and expense of metric tooling and equipment.

 

[Stan]

Anybody who is alive in North America today might as well get used to working in both systems for the rest of their lives. I have had two sets of mechanic tools for about forty years and still use inch tools more than metric. My 'old iron' machine tools are all inch while new Chinese stuff seems to something in between inch and metric (sort of a universal size). My brain automatically relates to inch measurements and I have to do mental conversions when given metric numbers.

The corner hardware store has common metric bolts and nuts but socket head machine screws in 6,8 and 10 only. When working in model sizes, it is a challenge to find all the sizes and styles in metric even though Canada has been officially metric for many years.

 

[DICKEYBIRD]

...one more piece of info for what it's worth. I too have a lathe with an MT3 taper and used it extensively for milling before I saved up and got an X3 mill.

For my 1st milling-in-the-lathe episode I put a 1/2" endmill into an MT3 collet, snugged up the drawbar and milled happily along until time to change tools. I had to whack so hard on the thing to get it out I was afraid I'd damaged the spindle bearings and probably did. Maybe it was due to a problem with the collet and/or spindle taper but it scared the crap outta me!

After that harrowing experience, I used my 3 jaw exclusively to hold various sizes of endmills up to 3/4" and never had any problems. IMO, the rigidity problems inherent in using milling attachments on a small lathe precludes tool creep issues. I just couldn't make a heavy enough cut to cause problems. YMMV

 

[Kermit]

So is there a difference in end mill holders other than price???????


I refer to the manual end mill holders with a MT3 taper shank costing 20 to 30 dollars and the manual Collet holders with MT3 taper shank, costing 150 upwards just for the holder, sets starting at $600 for chinese made.

http://www.use-enco.com/CGI/INSRIT?PMAKA=210-1234 (example)

I also have to bring my milling attachment in to work to have the inside of the forked tool post insert milled out to a larger dimension. The opening is about .07 inches to small to put into my tool post rocker.

Kermit

 

[Stan]

Kermit: I thin you are comparing apples and oranges. End mill holders are just that. they are made to hold Weldon shank endmills which have a flat on the side for the set screw in the holder. They only come in endmill shank sizes.

Collets are a different item. They are available in many different styles and many different sizes and many different prices. Almost all collets require a collet chuck which is available to fit the machine that you are going to use the collets in. MT-3 collets are what we have been talking about in this thread because they will fit directly into the MT-3 lathe spindle and no special chuck is necessary.

For hobby work import collets are usually of adequate quality and the price is very reasonable. If you want a full set of MT-3 collets (1/8"-3/4") you should be able to find them on sale for about US $100.00 otherwise singles for under $20.00

 

[Kermit]

Thank you Stan. I didn't know there were collets that had an MT3 taper. I've only ever seen the standard ER series, R8 and all those other Letter/Number names.
(I'm assuming these would be draw bar types)
Now I have to go searching my tool suppliers sites again... ;D


It helps to know it exists before you start searching,
Kermit

 

[Stan]

MT-3 collets are not the be all and end all of collets but they do serve a useful purpose. Unlike ER collets that are double tapered, the MT collets only grip at the front so there is not much size tolerance. That is: what you can hold in a 1/4" collet has to be very close to 1/4" but works well with standard sizes of bar stock.

My mill and lathe both have MT-3 spindles so I get double use out of a set I bought many years ago.

MT collets have a 3/8"-16 thread in the back end for a drawbar. When using a drawbar you cannot feed long stock through the collet. When I have to use long stock I have a collet nut to fit the threads on the lathe spindle. Shop made nut and hard to get a lot of squeeze because of the coarse threads on the spindle.

Any collet chuck for any type of collets that is held in by a drawbar will have the same limitation.