View Full Version : hss boring bars...

12-05-2010, 10:27 AM

Has anyone here made their own HSS boring bars out of HSS drill blanks? I've seen some posts about people bending them with a torch, and I've also seen some custom ground. I'm sure others start with a shank of mild steel and braze/weld a bit on the end.

I'm thinking of making a set for my boring head that has a somewhat adjustable length. I'm thinking if I make some 1/2" sleeve adapters for my boring head and then have it clamp different HSS drill blanks in it that can be adjusted in and out for different lengths of bore. I'm thinking of maybe an adapter for 1/8", 3/16, 1/4", and 3/8 drill blanks. Because these blanks will be straight diameter (up to the cutting tip), I can use them as adjustable length boring tools on my lathe tool holders as well.

So my question is this:

To make these blanks useful (i.e. have clearance) I will have to make a bend right near the end, or braze an offset piece in there. I'm not sure how close to the cutting end I can heat the HSS to make it bend without loosing hardness. I'm considering clamping the cutting end in Aluminum to protect it from overheating. I would think I could bend it a few diameters back from the cutting edge without alot of performance suffering. Maybe on the bigger stuff (3/8 and 1/4") I could use some of those set screw holders, either custom made or bought. I think the solid bars would be simpler though.

Another option would be a cheap source for headed HSS ejector pins from injection mold companies. My online sources showed that these are pretty expensive in the larger sizes. I can't help but think there are boxes of mistakes and scraps out there though.

This will mostly be for bores that are 1/2" and under. Anything larger and I'll probably buy a set of 1/2" carbide insert boring holders or use the HSS boring bars set screw style holders.


12-05-2010, 10:43 AM
I used a old exhaust valve from a cummins.


12-05-2010, 10:51 AM
I wonder if there is a source for small valves (3/16-3/8" stems) ? Also, what material, hardness and durability are these valves?


12-05-2010, 10:59 AM
Carbide endmills can also be used to make good boring tools using your approach.

12-05-2010, 11:05 AM
The stems of valves are soft enough to cut or file but the end of valves are very hard and can only be ground. I am unsure of what the actual material is but it seems to me it is very close to HSS. I haven't used it allot yet but the little I have used it it worked great and gave a nice finish.

The cummins valve in te pic is close to 1/2". Obviously smaller motors will have smaller valves. I think most american V8 valves have close to a 3/8" stem. I would think the smallest stem valve would come out of lawn mower motors.

12-05-2010, 11:09 AM
With the price for a set of HSS or carbide boring bars for boring heads for a mill so cheap it's hardly worth reinventing the wheel.

If your dead set on making some bars just braze or silver solder a piece of HSS cutter on the end of a piece of cold roll bar the sizes you want and be done with it.

That is, unless your just wanting to do something that will consume a lot of time.

12-05-2010, 11:14 AM
Total noob here, so maybe this is a dumb question, but why not just rotate your tool holder a few degrees counter-clockwise to get the necessary clearance? The cutting tip geometry would need to be adjusted to compensate, of course.

Rusty Marlin
12-05-2010, 11:18 AM
I've made a couple from O1 Drill rod.

I offset a piece of 1/2" in a four jaw and turned a 3/8" shank just less than tangent to the original surface. Then milled in the rake angle and back off angles, then hand ground in the clearances. The hardened and tempered it. Its works better than any POS Chinese carbide tipped boring bar I've ever used.

Took less than an hour to make.

loose nut
12-05-2010, 02:00 PM
Take on old 2 flute end mill of the appropriate size, grind off one of the flutes and sharpen the remaining tooth to the right shape for a boring cutter. works great, very stiff. Better then a round bar and a piece of HSS in it.

12-05-2010, 04:37 PM
Take on old 2 flute end mill of the appropriate size, grind off one of the flutes and sharpen the remaining tooth to the right shape for a boring cutter. works great, very stiff. Better then a round bar and a piece of HSS in it.

I have done the same thing, but with either broken end mills or just being sure to keep the tooth geometry on one side set right.

12-05-2010, 04:40 PM
You can use the two flute endmill as is with no grinding if it is sharp! Just get the point rotated so its level a.d adjust to center height in a boring bar holder.

12-05-2010, 05:30 PM

Please tell me where I can buy a HSS boring bar set that will cover these range of sizes. I've looked all over and the HSS sets are substantially more than the carbide ones. I don't have a diamond grinder at the moment.

Of course I am not looking to consume time. I like to collect tools that allow me to work with a full range of diameters and bore lengths without having boxes and boxes of cutting tools. This may be a ridiculous goal, but I thought it would be a cool project. I'm not in business so some of these tooling projects are fun for me.


12-05-2010, 05:34 PM

The reason I want the cutting end to be offset like traditional boring bars is so that I can use it in a boring head on a mill as well as a lathe. I honestly don't know what the disadvantage is to angling a straight shank tool in a lathe but it does sound possible.


12-05-2010, 05:54 PM
I don't think the ground endmill/tap/reamer will really work in this application. On the boring head you can't readily adjust the angle of the tool on the lathe. I also want the shank on the tool to be stright diameter right up to the cutting edge so I can either "choke up" on the tool (for rigidity) or extend it for lighter cuts on longer bores.

I think I need to start with a product that has a head on it (like the valve stems) or solder/braze/weld something on the end of some shafting (CRS, whatever). Any advice on how to grind the pieces for preparing to braze them would be appreciated. I'm thinking you would want to overlap them somewhat so that the brazing bond was strong and didn't tend to loosen with heat or anything like that.

I attached a picture for clarification. Its crappy as I don't have CAD on this computer right now. I think it conveys the point. The piece in the center is the cutting tool that can go into the headed bushing that has a clamp so that the boring tool can slide in and out. I was also thinking of using a set screw on to a flat on the boring bar so I don't have to set the rotation every time.


12-05-2010, 06:17 PM
Please tell me where I can buy a HSS boring bar set that will cover these range of sizes.

This is what you want-

12-05-2010, 07:22 PM
This is what you want-

That looks like a nice set of bars, but ouch I looked up a price and it was $277


I'd grind mine from solid before I bought these. :)

12-05-2010, 07:50 PM
That is the carbide set. KBC lists the HSS set (2H-235) as $126.85.

12-05-2010, 08:05 PM
What about using CR shaft and drilling a hole through it an using the shank of a drill bit. You could split the end and put a cap bolt to clamp the drill bit or cross drill and thread for using a set screw.

Haven't tried it, sound very inexpensive.

12-05-2010, 09:02 PM
It sounds like I need to learn how to silver solder because at these sizes using set screws is difficult. Maybe I'll crack out the Silicon bronze and experiment with the TIG welder.

12-05-2010, 09:49 PM
Tylernt. if you rotate the boring bar tip of the center line of the bore you will have lots of problems. If you rotate it below center line it will dig in and cause chatter. If you rotate it above center line it will be at a positive angle and makes it hard to machine in some metals.

The closest to center line you can get is best and it's true in a lathe or a boring head in a mill.

KEJR, for what your doing and for a low price just braze or silver solder some HSS on the end of a CR rod the size you want. That will be the cheapest and fastest way to do it.

12-05-2010, 10:00 PM
A single good quality 1/2" HSS boring bar is going to cost you $30. The good bars are a pleasure to work with and the cheap carbide sets just take up shop space. If you have any old carbide endmills you really should try making some into boring bars. You are going to need to be able to grind and sharpen both HSS and carbide.

In Randy's Pequil to HSS/Carbide thread he shows a boring bar he made to hold square HSS bits. You should take a serious look at it.

Everede make some good boring bars that take triangular bits of either HSS or carbide. They are very easy to sharpen.

12-05-2010, 10:06 PM
KEJR, for what your doing and for a low price just braze or silver solder some HSS on the end of a CR rod the size you want. That will be the cheapest and fastest way to do it.

Thanks Carld. Any advice on how to shape the HSS piece onto the rod? Should I attach it like they do on the carbide brazed tools, or can you just cut a chunk of HSS round off clean and braze it to the CRS bar end? Something tells me I should lap them to give more support and surface area for the solder/braze


12-05-2010, 11:19 PM
I just face the end of the rod and then braze or silver solder the HSS piece on so the top is as close to the center of the rod as posible. Then you have to grind it so everything clears a bore. You leave some of the HSS sticking out one side and that is the cutting part for boring. Be sure to have enough sticking out for future sharpening and bore clearance.

You'll have to get some 1/8" sq HSS to make the small bars with. Having some 1/8", 3/16" and 1/4" sq HSS on hand is nice to have for making boring bars when needed.

Bill Pace
12-05-2010, 11:32 PM
As mentioned, making up a boring bar, grooving tool, threading tool, or as in this pic, a pulley forming tool, is pretty easy. Its the crosswise one to do a set of step pulleys for a small belt. I just grab whatever is handy to use, in this case a piece of 1/2" key stock, Chucked it up in the mill and cut a 3/16" groove in the end, formed a piece of 3/16" HSS lathe bit to the pulley dims and stuck it in the slot and brazed her up.

I really cant remember what I made up the other one for:confused: ... but, here again, I just plowed a groove down a piece of round stock and brazed the bit in.

To do a boring bar the same would apply - I had one, -that I couldnt find, - that I had made the slot deep enough to allow to braze a plug on top of the bit and put a set screw in allowing changing of the bit/


12-08-2010, 09:49 AM
Machinistís Workshop Dec 2010-Jan 2011 pg. 34 has an Article by Steve Acker re Modifying a Bullet Mold. There are good pictures and directions for making a HSS boring bar.
The size of this example is similar to that sought in the beginning of this thread.