The question about drawbar for milling machine.

Hi folks!

I has the new milling machine Zhejiang ZX-25 in my house.

The question about how much torque or angle i need to fasten the milling tool who has Morse taper #3?

I learned out it's not easy to knock out the milling tool with hammer on drawbar.

Also i am very afraid if the rolling bearing will be damaged.

Hi Jens Erik,

Congratulations with your new toy. My milling machine also have a MT 3 taper, I don't use much torque to fasten the drawbar. I hold around the bottom of the spindle with one hand and the other on the spanner, I even don't use the whole length of the spanner. I have never had any problems with the toll coming loose. As you have already found, to much torque makes it difficult to knock the tool out.

Thor

Thanks.. Yes, i has allready learned out it's not neccesary with much torque to keep MT 3 on place..

Also let us say when we are tightening the drawbar not more than it will hold the MT3 on place to example not more than 1/4 of the whole turn on the drawbar?

There are alternatives to hammering on the drawbar. Firstly do not use a steel hammer as that will likely damage the bearings - only use a softer metal hammer like a copper faced mallet. One alternative is to drive wedges between the tool and spindle shoulders.

As above, the tool only needs to be retained to prevent side thrust of the cutting tool from loosening it. Drilling does not tend to loosen the tool.

Do make sure the tool is not colder than the socket when inserting - expansion of the tool, on warming to the machine temperature, can severely tighten the fit! Think here of shrink fitting

Thanks for explaining.

This appears to be a standard round column mill-drill.

1/4 turn is quite a lot. Use the pitch of thread to calculate the amount of movement a 1/4 makes in length. Tha tis how much you have stretched the drawbar.
Wind down the quill and look for the slot in it that allows you to see right into the spindle and into the inside of that which allows you to see the top of the tool. You can get a wedge that goes into this slot to push out the tool. This slot is common in pillar drills and most of these mills too.

If you do end up having to hammer the drawbar try to provide support between the end of the spindle, not the quill, down to the table to take the force off the bearings.

Also if you suspect the problem is due to the tool / spindle heat difference mentioned above run it for a while to heat up the bearing.

Edited By Bazyle on 19/11/2017 09:05:55

My Rexon (Naerok in UK) mill has a #3 MT, the spindle nose is threaded, and there is a nut to retain the #2 MT adapter, I leave that in place, and to drop milling chucks etc just unscrew the nut and this pushes the item out. Don't know if this is proper procedure, but no one has told me other wise(I'v never asked any one). The slot on the spindle is only for removing the likes of a Jacobs Chuck with a MT with a tang on it.

Ian S C

Get or make yourself a taper cleaner for the inside of the taper. Make a wooden taper about a millimeter less in diameter and glue three strips of felt down the length, eliminates any debri in the taper. Goes without saying wipe the male taper as well.

I use a plastic lead loaded mallet ( Quite a small one) and one tap disengages the taper.

Clive

Is it possible to make a captive draw-bar adapter like this:-

Saves a lot of hammering and much kinder on the bearings. This example from *** mikesworkshop *** is for a smaller mill.

See also this ***Thread***

Enjoy your new toy

John

Edited By Journeyman on 19/11/2017 10:28:09

My mill also has a 3MT and I lower the quill onto a wooden block to support the underside of the spindle to take the load off of the thrust bearing while tapping the drawbar with an aluminium head mallet.

If too tight, I use a wedge clamp to remove the cutter. (Details were published in MEW. Can someone remember which issue). Paul.

+1 to that. The drawbar is mainly used to stop the tool being pulled out of the taper. It also allows the operator to pull the tapers together with just enough force to stop the tool spinning in the spindle; no more! It's easy to over-tighten the drawbar so the two wedge together and are hard to separate.

On my mill there's not much difference between too loose and too tight. After experimenting I now hand tighten the drawbar and only add about 1/8 turn with a spanner, perhaps a little more if using a large milling cutter.

One or two sharp taps with a 1kg hammer cushioned with an Aluminium block are enough to release the taper. Sometimes it's harder. I blame work, like drilling, that pushes the tapers together or putting a cold tool into a hot spindle. I'm not too worried if it sometimes takes 4 or 5 sharp taps to shift it. If it regularly takes more than that, the drawbar is probably too tight.

Dave

I have a WM 16 mill which has a captive draw bar top hat that screws onto the spindle & ejects the collet chuck, or any other tool fitted, when the draw bar is unscrewed it bears against the underside of the top hat & pushes the drawbar & chuck down then simply unscrew the drawbar, does away with any need to use hammer. As for tightening, I use a 1/4 drive ratchet & just snug it up... no more than 1/16 turn once I've screwed the drawer bar in finger tight, I find that is quite secure enough.

​George.

Also if you suspect the problem is due to the tool / spindle heat difference mentioned above run it for a while to heat up the bearing.

This action will be too late and not help if a cold taper has been inserted into a warm socket - the tight fit will be achieved as the colder part warms to the same temperature as the machine. Any temperature change after that will result in both the socket and tool changing size together (same delta T). Shrink- fitted parts do not come loose easily, by changing the temperature, unless their coefficients of linear expansion are suitably different.

Funnily enough, I made the components for a new headstock drawbar for my S7 yesterday - so that's MT2. I'm not planning to apply any more clamping torque than I can manage with a knurled thumbscrew. Outer is located to teh shaft with a grubscrew, and simply allows me to screw the bar into the arbor. Inner thumbscrew then applies clamping torque. There is a stepped bush below that, which centralises the drawbar in the mandrel.

Cheers, Colin

Many useful to read the comments .. Not even 1/4 to twist the draw bar, really even less .. Read that one wrote that it's enough to turn 1/16. While the latter man only uses his fingers to twist the knurled nut.
I'm thinking if we can use a spring-loaded ratchet or a friction sleeve to turn the drawbar without tightening too much on draw bar the same principle we use on micrometer?

You do need to put some elastic load into the drawbar if the cut is intermittent. (I am not suggesting tight + 1/2 turn on a 3/8 BSW) Otherwise, it is not unknown for the taper to work loose..

If the drawbar is not captive, it it possible to make a small mod allowing an extractor to be fitted to the top pulley to exert pressure on a slackened drawbar to break the Morse taper. Unless you have really tightened the drawbar, it should not be necessary to even give a light tap to such an extractor, when it is exerting pressure.

1/4 BSF, / UNF or M6 can apply enough end load to break a 3MT taper fairly easily.

Howard

My simple self-releasing drawbar for X2 mill:

www.model-engineer.co.uk/forums/postings.asp?th=63585

Little 8mm square used for tightening, has never come loose.

Neil

My milling machine has M12 drawbar and i has created the 2 other drawbar M10 for boring head and 1/2-12 for ER32 collet shank. I'll try to see if I can fit the extractor to the milling machine so I do not have to knock on the drawbar.

Hi Jens

Check my albums for all size lock bolts

Eric

There is not much material to mount the extractor to drive out the MT3 tool out of spindle.. The outer diameter is 21,8 mm and the hole inside is 12,7 mm (1/2" ) . Do you have the idea?

I learned out the wedge can not drive out MT3 tools due the length is shorter than standard MT3.

Edited By Jens Eirik Skogstad on 23/11/2017 21:36:03