Homemade Draw Bar

I need to make a draw bar for a garage sale piece of equipment I picked up cheap recently. Its got a drill chuck and a metric draw bar, but it won't
work for the collet holder I want to use instead of the chuck. The collet holder has the right taper, but uses a 3/8 draw bar. There is only about 1/4 or maybe 5/16 passage through the spindle for the draw bar.
I figured to get a piece of rod, thread both ends with some standard threads, and make a theaded bushing to loctite onto one end to go in the collet chuck. Then make a knob to go on the other end to make it easy to loosen if I ever want to take the collet chuck out. Something easy to hit with a hammer instead of slipping of and smacking a pulley.
(The draw bar holding the drill chuck taper was similarly configured except metric and just had a nut.)
I can't think of any reason to get overly obsessive compulsive over it, but I thought I'ld ask you guys if there was any reason I needed to go ape over balancing it or getting my bushing highly accurately concentric? This machine spindle is relatively low speed. Top speed is 3840, but I don't see me using it at that speed very often. I just plan to use it for the occassional manual milling operation that I can do faster by hand than to write a snip of code for one of the CNC machines, or for when I have a project going on the machines, and have something else I want to try.
With it basically going through the axis of rotation it would take a pretty significant imbalance I am thinking to cause any vibration. That and it doesn't have anything holding it EXACTLY centered at the top end anyway. I suppose I could make the knob with a slight taper to do that if I wanted to, but I think I would rather have a flat washer in between to protect the surfaces. Speaking of washers, Since the taper is actually holding the chuck. Any reason to need a spring washer under the knob?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bob, I assume you bought a used Chinese Mill/Drill. They normally have at MT3 Quill taper or some of the newer ones have an R8 spindle. I assume you have the MT3 variety. In Europe the tool for these machines use am M10 thread. In the US those tools use a 3/8-16 UNC thread. The purpose of the drawbar is to prevent any helix in the cutter from pulling the tool holder out of the quill. I too had to make a draw bar. It is no problem to do. I used a 3/8 rod. threaded one end and pinned a piece of 3/4 hex stock drilled for the rod on the other end. Be sure to use two pins, not just one. Tighten lightly or you will shear the pins. It just needs to be snug. those mill drills are incredibly handy. I wouldn't be without one, but like everything else from China, there are good ones and bad ones. Steve

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

P.S. While not an Iggy or Gunner class score I paid less for the mill than I did for the collet chuck. I hope it was worth it. LOL.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think the hex and pins bit was a way to avoid the threading and to give an end that could be tightened with a wrench. Good idea for R8 or NMTB tapers. Overkill for Morse tapers.
If the hole in the spindle is big enough that the drawbar could be off centre, then instead of making the end of the hand knob tapered, make it with a pilot that is a good fit in the bore. You can still have a flat face for the thrust, but you get centring as well :-)
Mark Rand RTFM
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Good idea Mark. I like it. Wound up not finishing the draw bar today. I got distracted by a loose gib on the machine and discovered one of the gibbs was missing a specialty adjusting bolt. Instead of finishing my draw bar and knob I made a bolt for adjusting the Y Axis gib in and out. LOL. No ADD in my familly no sire... Ooh! Bright and shiny.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sounds just like my Emco lathe/mill. The mill uses a MT2 collet with an adapter to mate with a metric drawbar. look at the Yahoo EMCO lathe news group. Lost of posts about the adapter there.
I can send you the specs of the adapter if you wish.
Paul
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks Paul, but I can measure it up and make it this afternoon with no problems. I was mostly curious if there were any snafus to watch out for. I'm already half done. Was just taking a soda break.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The only snafu to watch for is to cut a groove in the bottom so a screwdriver can get up into the bottom and hold the adapter when the collet unscrews from the adapter before the draw bar unscrews.
Paul
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I had not thought of that. It's a good thought. On this application I do not think its necessary as the draw bar can drop out the bottom of the machine after removing the knob/nut on the top if the adaptor does stay on the draw bar. It really doesn't matter if the adaptor bushing unscrews from the chuck taper or the rod unscrews from the adaptor bushing.
Anyway, I finished the draw bar and thread bushing yesterday. I also made a different bushing for the original metric threaded taper on the drill chuck. That way I can leave the bushing in the taper, and I don't have to keep track of a separate draw bar. I promptly threw the original draw bar in the trash. The only drawbar now for the machine is always in the machine.
I can leave the adaptor bushing screwed into its matching chuck when not in use.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.