View Full Version : Mill Advice Needed

01-31-2010, 01:12 AM
I've been building Hodaka swing arms for what seems like forever now. It's been a very educational process to say the least. I think I must like not knowing what in the hell I'm doing. I do it all the time!

My current issue is I'm not real happy with a boring jig I made for them. When I weld the arms onto the pivot tube it distorts to the point where it won't accurately accept a bushing anymore. The jig allows me to bore the ends of the tube. Here's a pic.


I guess I can say this jig is functional in that I can use it to gouge out bores at either end that are at least pointed at each other. Gouge being the operative word. What happens is I have to push on the drill to the point where the bit gets under and cuts, but then it's off to the races for a short distance. I've got the bit ground to cut in either direction and a larger radius has helped, but man .... is it ugly in there.

The other difficult issue is setting the bit extension to control the dia of the bore. I made this doodad to help.


Being able to use the setscrew to push the bit to where I want it has helped, but I still haven't got good enough control. I'll probably wind up having to make a custom fit bushing for every arm.

Meanwhile, a Seig X3 recently found it's way into my shop from Harbor Freight by way of a 20% off coupon, and it occurred to me maybe the mill would be a better way to go. Having absolutely no milling experience until the X3 arrived it's entirely possible I could be completely wrong, but I chucked in a vise and snapped a pic to give you guys a general idea.


Tooling for the little mill is just about non-existent. A small sampling of R8 collets and that giant 6" vise are about all I got. I could build an alignment fixture to bolt to the bed tho, or I could buy whatever tooling :) .... lol. All I need is an excuse.

So what would you guys do?


01-31-2010, 01:20 AM
Perhaps post a pic of your line boring bit.
I suspect it could be as simple as sharpening it a little different.
I do like the babbitt bearings for the bar.


01-31-2010, 01:53 AM
More than happy to Doozer, altho I'm not real proud of my bit grinding. Especially this one! It's so small it's really hard to hold.

Top view.


Side view.



01-31-2010, 02:00 AM
Make an L bracket and use most of boring bar set up in mill vertically.

A little more time grinding will make a world of difference in cut. :)

Should look just like a lathe tool, but with more front relief for bore...

No threads being cut there, round that tip off..

You could just add relief to a factory ground tool.

I often use round tool bit stock for boring bar work... Does make it tricky to grind a round to a needed spline shape though...

Make bit pusher threads 20 or 40 TPI for the mike effect. An old bridgeport quill stop is already marked on OD for thousandths... 20 TPI :)

A special similar tool, can be made to indicate bit protrusion...

Still a bit of cut and try...

01-31-2010, 02:04 AM
looks like the line boring jig would work. I think the bar may be to big it dosen't look like there is enough room for your chips to clear the tool bit. The chips could be building up around your cutter causing issues. Do as Doozer sugest post pics of your tool. And maybe use your new mill to machine a flat on the boring bar to give the chips some where to go.

01-31-2010, 02:07 AM
After seeing your second pic it looks like you should have enough chip clearence

01-31-2010, 02:50 AM
You really need some sort of feed arangement just not enough control with hand feed . your tool could use a litter better grind don't make quite so much point other wise it looks like it ought to work. A little air to clear the chips should help to.

01-31-2010, 04:00 AM
For setting the boring bit, you could make a boring bar micrometer, similar to


Easy to fabricate out af a bit of angle iron, with some plate welded on top of it. Set plate vertical and on centre and bore and tap say 40 tpi.

Note the loop/hole on the top - unless you have three hands this is useful so you can cable tie the thing in place while adjusting the bit.

Remember that a thou' on the micrometer is two on the bore.

If all the bores are the same, forget the screw. Let the plate hang down 'too much', take a trial cut, measure the bore and then just shorten the plate to suit.

Third method is a piece of tube with ID=boring bar dia. + bit projection. May need notching to allow access for bit clamping screw. Make a small cradle for it to sit on at the powered end of the bar and it can stay on the bar.

On the feed issue, clamp a shaft collar, a thrust bearing and another (free running) collar to the unpowered end of the bar and you have something to pull against for a more regulated feed. For example, weights and pulleys (c.f. various bandsaw feed mechanisms posted in the past), groove the collar and use a lever feed, mill (circular) rack teeth into it for a leadscrew or a gear.

01-31-2010, 11:02 AM
Thank You for the discussion and the advice gentlemen. The general consensus seems to be there's nuthin' wrong with the jig, so I'll keep working on improving it.


01-31-2010, 11:23 AM
Are you building the swing arm off of the tube on the jig or are you building the swing are first than welding it to the tube on the jig?

You should be building the swing arm first and than welding it to the tube on the jig otherwise it will distort every time. Lots of tack welds to the tube. Than short welds only. Weld about 1/2 inch at a time alternating from side to side. Let cool between welds.

true temper
01-31-2010, 11:55 AM
Your tool bit needs some work, thats a lot of the problem. It looks like it has a lot of neg. rake to me. The boring jig looks much better than some I have come up with, I think you are on the right track. To set your bit, drill hole in bar almost all the way through with dia. so you have a sliding fit to your tool bit. Cross drill for a set screw to lock in place. Put a small spring in the hole to push the bit out. I have used a brush spring out of a delco altenator. Then you can set the bit with a mic. Loosen the set screw and the bit will pop out against the mic face.

01-31-2010, 01:01 PM
Your boring rig looks good to me. Can you use a insert? Easier and you'll have consistent results.
This was my hand fed rig to bore the headstock on my SB9 and it was a interrupted cut to boot.


the weapon, ccmt lathe tool in 1" bar-

Let's see what we can build ..hmm I got this and that and one of them-

The aftermath-


01-31-2010, 01:05 PM
I am curious, did you just slide the headstock along the ways to do the cut or did you mount it to the carriage somehow?

01-31-2010, 01:08 PM
vpt, on my welding jig I mount the tube and the 2 axle plates first. The relationship between those 3 objects is what the whole deal is all about. I use alignment bushings in the tube to center it on the fixture and on one of my earlier attempts the bushings seized from welding distortion. Carld suggested split bushings and that solved that problem. If I mig the tube goes out of round around .005. If I OA weld it it's a much as .015.

Neither will accurately accept a bushing, hence the boring jig.

Along the way I've also found I need to space the axle plates an 1/8" out over nominal because they always warp in.

It's been a learning process ......


01-31-2010, 01:18 PM
I am curious, did you just slide the headstock along the ways to do the cut or did you mount it to the carriage somehow?
Head stock was slid to the far right of the bed where there was no wear and tightened down. I used a rig mounted to the lathes carriage and used the rack to hand feed it.

01-31-2010, 01:18 PM
True temper, it does have negative rake. I thought being an inside cut it was supposed too! I've been thinking to try a flat top bit, but I was worried about the tip of the bit being on the centerline of the bar. Maybe that's not too important.....

And I got lots of Delco alternator parts from a previous project. Spring loading sounds like a wonderful idea. Where is all that junk?:)


01-31-2010, 01:36 PM
SJH. I remember that post. Dude, you are so far above me we could be on different planets!

Something I probably haven't explained well enough is that I'm only boring 1.5" deep on either side. The pillow blocks split so I just do one side and then open it up to reverse the bar.

Considering I'm only needing 1.5" I had another thought for better hand feeding after taking a look at the lever operated collet closer for my lathe. It has a single link on the back side with 2 pivoting ends. One end would mount to the jig. The other end connects to a bearing housing with the ID of the bearing fixed to the boring bar. And on the my side of the bearing housing I could mount a big ol' long lever. The ID of the bearing would spin with the bar while the OD would move back and forth with the lever.

Might work .....


true temper
02-01-2010, 01:13 AM
Try drilling your hole in the boring bar a little off centre. Then grind some pos. rake on your bit and try that. Let us know how it works out.

02-01-2010, 07:27 AM
I find a standard (cheapo) boring bar makes a handy 'holder' for your HSS bit as you grind it. Other tools that work: vise grips, custom made clamping blocks (Slited, set screwed, whatever), Sometimes its easyer to clamp it in a vise and take the dremiel to it, pertty much ANYTHING that grinds metal can be used to shape tiny HSS bits with reasonable success, just keep lots of water handy to keep it cool.

Small HSS bits are cheap and come in long bars that you can often cut in half or thirds for boring bar use, So go crazy praticeing and trying out diffrent grinds! Google for info about grinding and try out some basic tool profiles. (Small radius, big radius, no rake, rake with chipbraker, etc)

Its the big HSS bits that are a pain.

Paul Alciatore
02-01-2010, 09:51 AM
Rigidity is important. Be sure your clamps have a firm grip on the tube. And the unsupported ends that are just sticking up in the air worry me. They are essentially a tuneing fork and are probably vibrating while you cut. This can't be good. If you could rig something to clamp them down it may help.

Also, it is not completely clear that you have enough clearance on the bit. It is certainly OK just below the cutting edge, but the bottom may be scraping. It may be worthwhile to grind a secondary clearance on that bottom side just to be sure.

And make sure that the bit is dead sharp. Use a fine hand stone to touch it up after grinding it.

Chip control. Chips are what will ruin the finish inside a bore. They get caught in the bit and make grooves. Side rake on the bit can help by aiming them away from the cutting area. Also in cramped quarters, like inside a bore, taking light cuts and cleaning out the chips after each one will help. Your final cut should be only one or two thousanths.

Finally, some kind of feed screw would be a very good idea. I posted some pictures some time back that showed the difference that a smooth feed can make in the surface finish. And both before and after pictures were done on a lathe with the cross feed. Only difference was a longer handle for a more uniform feed. The more uniform the feed, the better the finish.

02-02-2010, 01:52 AM
Thanx again guys. I've got a new piece of drill rod on it's way for a new boring bar. Gonna go back to a 3/16" round bit which I initially had better results with. Because I was having problems with setting rotation and bit extension at the same time with the round bit, I gave the square bit in a round hole option a try, and that may have caused a lot of the problems. A .359 hole to clear a 1/4" sq bit most of the way thru a .750 bar can't leave much strength right where the cutting forces are.

I will absolutely spring load the bit. That works. And you don't have to drill all the way thru which leaves a much better surface to measure from on the back side.

I've also started the design and constuction of a lever operated feed. We'll have to see how that works out but at least I'll have a good time making it.:D

Thanx again.