How do you make a D-bit?

I tried to search "D-bit" but it told me there were no matches, which is odd since I saw it mentioned several times when I searched "taper reamer".

What I want to do is ream the ID of some DOM tubing to a 2.25"/foot taper, roughly 1" deep and 1" ID at the large end. I'm making sleeves to fit the taper on the end of a motorcycle crankshaft and will be doing the work on a turret lathe. The closest off-the-shelf taper reamer I can find is 2"/foot. Before I shell out the money for a custom reamer, I'd like to make a handful of parts to test the market.

D-bits were mentioned in other threads but with little detail on how to make them. In one post it said to turn a bar to the desired taper then mill off half of it. That sounds easy enough but how do you put a relief on it? Does it need it? How well will a D-bit made from O1 work on the steel tube? Could I get 10 parts out of it?

Here is a simple method:

D-bits

As to your other questions, you will have to try it and find out.

-DU-

IME DOM tubing can be awkward stuff to machine on a good day, however;-

On larger diameters, bear in mind D bits can only be regarded as finishing tools.

Clearance;-

I know it sounds a bit hit and miss and I don't understand the geometry etc of it, but the clearances seem to sort themselves out and the tools work, albeit slowly.

For your application I would make a piloted D-bit,(like a counter bore) and run a parrallel boring op first to guide the D bit and reduce chatter.

The board search function fails to search on short terms.

Google is a better way for short terms.

practical machinists d-bits - Google Search

Which will give you:

http://www.practicalmachinist.com/vb/gunsmithing/d-bits-127324/

http://www.practicalmachinist.com/v...-mills/d-bit-cutter-grinder-sharpener-156647/

http://www.practicalmachinist.com/vb/general/d-bits-154906/

I thought D bits were meant to be used to make nice round holes in non-ferrous sheet or plate, but what do I know I'm just a humble clockmaker.

Rich

richmccarty said:

I thought D bits were meant to be used to make nice round holes in non-ferrous sheet or plate, but what do I know I'm just a humble clockmaker.

Rich

Click to expand...

Seems the earliest history is bagpipe-makers tooling.

richmccarty said:

I thought D bits were meant to be used to make nice round holes in non-ferrous sheet or plate, but what do I know I'm just a humble clockmaker.

Rich

Click to expand...

They also were and are used to produce forms within a blind or stepped hole. For instance many old time gunsmiths made their own chamber reamers, they used D reamers (I was taught they were a D reamer not a D bit).

Bill

Also called a toolmakers reamer. Here is one I made from a piece of drill rod http://i72.photobucket.com/albums/i163/miltons_stuff/reamer.jpg

I think boring would be better, especially on tubing which is not going to be perfectly concentric inside and out.

That's D-bit?

Winfield said:

Also called a toolmakers reamer. Here is one I made from a piece of drill rod http://i72.photobucket.com/albums/i163/miltons_stuff/reamer.jpg

Click to expand...

Your picture is a different type of reamer than I think is usually referred to as a "D-bit.". D-bits are made by grinding or milling a step almost to a diameter line of a round piece of tool steel. The step is shaped a little on its leading edge but is not a diagonal straight grind as shown. I know the reamer you show is design that is useful and I am not putting it down. But it has a different application than what I believe is a D-bit.
I comment just to avoid possible confusion.
Denis

A good source

Is there a good source of information on how deep to grind the "D" portion of the reamer down? I am interested in making a D reamer for making precision holes in aluminum blocks. What is the optimum angle for the cutting side against the aluminum work? What is an ideal material for the reamer to be made from?

Does anybody know a textbook or table that could be helpful here?

Thanks in advance!

Hi

I have made a D-bit reamer from a piece of 1/2 inch HSS round. I am having problems because the hole is tapered at the cutting end. The reamer is cutting an undersized hole and jamming the reamer as it progresses. The D-bit flat is currently a couple of thou above centre.

I have seen questions raised about grinding relief below the cutting edge, but few authoritative answers. I found these instructions below at this site: D-bits


We use to have some guys who were a real wizz with D bits, we use to make hundreds of dies a week with D bits, the D bits were made from HSS and one of my jobs as a grinder was to make D bits getting the curved form correct was a bit of a fiddle, but once you mastered the method, it was quite easy, once the form was ground, they were sectioned a couple of thou over centre then they were backed off on the cutting side so that there was 10 thou land, then the turners would slightly hollow grind the top free hand, when it came to making the die they would rough the form out with a form drill that they had ground up free hand, followed by a roughing D bit, the D bit wasn't held in a chuck but was supported on a fixed centre in the back with a carrier bearing on a steel block to stop it turning, the roughing bit was then followed by a finisher, the turners had an oil stone same as a carpenter uses to keep the Bit sharp, as far as I can remember each D bit would cut about 50 dies.

With the advent of spark erroders that could make dies out of TC that last 1000 of times longer, the skill with D bits was gradually lost.

As I understand these instructions, some metal is ground away from the area below the cutting edge to leave a 10thou land, something like on a drill bit (see sketch). I haven't ground any relief on the round part of the D because I was concerned about swarth getting into the relief, then getting jammed at the bottom edge of the relief.

The hole I am trying to ream is blind, so I can't use a regular reamer.
The exact hole size is not important because I will machine the bar to match the bore.
I just need a hole that has a good finish and parallel sides.

My thoughts are that if I grind a relief and 10thou land, this will cut a hole a little larger that the D-bit and stop it jamming as it does now.

Any suggestions?

Dazz

How deep is your hole?

You did not say how many diameters deep you are reaming. If you are reaming at least a couple of diameters or more, then you may be jamming because the shaft of your D-bit is not perfectly straight. So, provide some relief, but not under the cutting edge as shown. Provide the relief a diameter or 1.5 diameters down the shaft of the cutter toward the chucking end. Continue that relief as far as the tool will enter the work. It does not need to be much--probably just a couple thou. You should be able to determine the shaft crookedness with a DTI and the cutter chucked in your lathe or mill. I would not relieve the chucking portion of the bit as you likely would introduce error. After al, the relief could be provided with just a belt sander or off-hand grinding.

Using a 1/2 " diameter reamer, you will end up with a tool that is about 4.5 inches in total length and has the standard d-bit geometry for the first 3/4 inch or so. Then it will be necked down a couple thou for say 2 inches if you are cutting 1.75 inch deep holes. The last inch and a half will be untouched and this is the portion that will be in your chuck or collet (but only gripping a half inch or so of the tool may allow it to follow the hole better than gripping it for 1.5 inches and forcing it to follow the error introduced by chuck unstraightness.) The shaft relief idea is often not mentioned in write-ups of D-bit making.

In a perfect world it would not be necessary to provide the shaft relief I have recommended. But in the hardening process the shaft likely distorts a little bit along its length. BTW, you only need to harden the first half inch or so sf a 1/2 inch cutter. Heating and quenching the rest of the shaft is just asking for more distortion. This will be more pronounced with W-1 than O-1 (I always make mine from O-1 for this reason).

I only ask my D-bits to clean up a few thousandths on the hole diameter. They are not intended to remove a significant amount on the diameter, though, in a pinch, I have used them to flatten the bottom of drilled holes.

Hope this is some help.

Denis

dazz said:

Hi

I have made a D-bit reamer from a piece of 1/2 inch HSS round. I am having problems because the hole is tapered at the cutting end. The reamer is cutting an undersized hole and jamming the reamer as it progresses. The D-bit flat is currently a couple of thou above centre.

I have seen questions raised about grinding relief below the cutting edge, but few authoritative answers. I found these instructions below at this site: D-bits


We use to have some guys who were a real wizz with D bits, we use to make hundreds of dies a week with D bits, the D bits were made from HSS and one of my jobs as a grinder was to make D bits getting the curved form correct was a bit of a fiddle, but once you mastered the method, it was quite easy, once the form was ground, they were sectioned a couple of thou over centre then they were backed off on the cutting side so that there was 10 thou land, then the turners would slightly hollow grind the top free hand, when it came to making the die they would rough the form out with a form drill that they had ground up free hand, followed by a roughing D bit, the D bit wasn't held in a chuck but was supported on a fixed centre in the back with a carrier bearing on a steel block to stop it turning, the roughing bit was then followed by a finisher, the turners had an oil stone same as a carpenter uses to keep the Bit sharp, as far as I can remember each D bit would cut about 50 dies.

With the advent of spark erroders that could make dies out of TC that last 1000 of times longer, the skill with D bits was gradually lost.

As I understand these instructions, some metal is ground away from the area below the cutting edge to leave a 10thou land, something like on a drill bit (see sketch). I haven't ground any relief on the round part of the D because I was concerned about swarth getting into the relief, then getting jammed at the bottom edge of the relief.

The hole I am trying to ream is blind, so I can't use a regular reamer.
The exact hole size is not important because I will machine the bar to match the bore.
I just need a hole that has a good finish and parallel sides.

My thoughts are that if I grind a relief and 10thou land, this will cut a hole a little larger that the D-bit and stop it jamming as it does now.

Any suggestions?

Dazz

Click to expand...

Hi

The hole is 90mm deep and I need to ream down to about 60mm depth. The remaining 30mm will house a spring.

I ground some relief down the length of the D-bit. Didn't make any difference.

I am using a ER32 chuck to hold the 1/2inch round HSS d-bit, so I know it is centred. Just to be sure that the tailstock is centreing the d-bit, I tried reaming by hand. The bit still jammed.

To minimise grinding, I had made the length of the Dee quite short. The Dee is now about 1/2inch long. Regrinding the D-bit in this way still didn't make much difference. With the reground tool, I was able to go another 3mm or so before jamming. I am now down to about 25mm depth.

Blueing the d-bit showed that there was heavy rubbing behind the d-section, but not on the relieved length of the tool shaft. The bit is either skewed in the hole, or cutting undersized. I now suspect that the hole may be slightly banana shaped causing the tool to jam in the curve.

Dazz

Picture

A few pic of your blued bit might help. Also a pic of the shavings the bit is generating could help. Also what material is being reamed? Lube? I assume you are using a cutting oil.

How much material ore you removing with the D?

You cannot touch the outer diameter of the reamer when sharpening it or it will not cut to its periphery and jam. You do need a little end relief peaking at the cutting edge. You can put a small radius on the cutting tip but be careful of the angle of the edge. You can sharpen by using a lap flat on the ground portion of the D.

Somewhere something is not quite right. It should work in the application you are trying to do.

Denis

dazz said:

Hi

The hole is 90mm deep and I need to ream down to about 60mm depth. The remaining 30mm will house a spring.

I ground some relief down the length of the D-bit. Didn't make any difference.

I am using a ER32 chuck to hold the 1/2inch round HSS d-bit, so I know it is centred. Just to be sure that the tailstock is centreing the d-bit, I tried reaming by hand. The bit still jammed.

To minimise grinding, I had made the length of the Dee quite short. The Dee is now about 1/2inch long. Regrinding the D-bit in this way still didn't make much difference. With the reground tool, I was able to go another 3mm or so before jamming. I am now down to about 25mm depth.

Blueing the d-bit showed that there was heavy rubbing behind the d-section, but not on the relieved length of the tool shaft. The bit is either skewed in the hole, or cutting undersized. I now suspect that the hole may be slightly banana shaped causing the tool to jam in the curve.

Dazz

Click to expand...

I used to buy D-bits all the time for use in my screw machines they were called
half-round drill bits & still have a bunch great in brass or aluminum.
Like these
Amazon.com: Half Round Drill Bits - Fractional Sizes 31/64" (.4844) 4-3/8 LOC x 5-7/8 OAL HS HALF ROUND JOBBER DRILL: Industrial & Scientific

Hi

I am modifying drilling/reaming a Chinese 3MT arbor. I expect the steel is just ordinary hardened CS. I tempered it to blue to soften it. It machines well in that state.

The D-reamer is removing about 0.25mm from the diameter. I have not relieved or touched the side cutting edge. All cutting edges are honed sharp.

Initial cuts were at 60rpm but the finish suffered from BUE. I raised the speed to 400rpm and eliminated the BUE. I use oil to keep things lubricated.

I notice that most D-bits have a flat that is multiple times longer than the bit diameter. Does this allow the bit to flex down slightly to create a hole slightly larger than the full diameter of the shaft? The flat on my tool is about 12mm. Not enough to allow any significant flex of the flat part.

I am getting chips off the tip of the tool and no chips from the side edge, as expected.

Every bad tradesman blames their tools which is why I reworked the D-bit. I am now wondering if the workpiece might contain chromium. If it does, then what I am doing will work harden it in a flash. I am going to try reaming a piece of MS and see what results that produces. My lathe has developed an electrical fault which I will need to fix before any further testing.

Dazz

Pics?

Dazz,

Any possibility of seeing some pics?

I don't think my D-bits flex appreciably as they have about a 1:1 ratio of grind back to diameter. I think the intention is not to flex but rather to index in the cut and to use the cut to guide the bit. In other words the round ungrounded portion of the bit rides in the D-bit-enlarged hole as the leading/cutting edge makes room for the rest of the bit to follow.

I would be happy to be corrected if this is not an accurate assessment.

Denis

Hi
Attached are some photos.

The first version of the D-bit was very stubby to avoid too much grinding.
The modified version looks more conventional. What cannot be seen is that the shank is relieved from about 1/2inch from the D-section.

If the shank beyond the D-bit doesn't contribute to the way the tool works, then I guess one option is to reduce the shank diameter all the way up to the D-section.

Dazz

Thanks for the pics

Dazz,

Bit number two looks a lot better.

I do not think I would suggest relieving all the way to the D. I'd leave the first one inch or so of this 1/2 inch reamer full diameter. I do think the having the cutting end nest in the reamed hole for at least a couple of diameters is important. If the shaft of the cutter were perfectly straight and your tailstock *perfectly* centered(not likely), then no relief would be needed.I see you are using M2 HSS for your cutter. I would think that would be very straight if ground by a reputable manufacturer.

My main question on looking at your reamer is just how sharp is the flat of the ground-away portion? I cannot see signs of this having been sharpened with a fine (diamond?) stone. Maybe it is there and I just cannot see it. But it should shave your thumbnail if it is good and sharp. It also looks like the leading edge flat (end) could have a negative rake angle for a mm or so.

I often try to grind the horizontal flat (parallel to the long axis) hollow just a bit so that the lapping stone sits nicely on the shoulders of the hollow and does not rock as you sharpen. And the same is true for the leading edge end of the bit that is 83 deg or so to the long axis of bit. They both should take only a few strokes if the flat is ground right. A slight rounding of the nose is the final step in hand stoning being careful to keep the relief angle correct.

One interesting test would be to try this cutter as a boring bar. What I am suggesting is to put a piece of scrap 12L14, 6061, A2 or a KNOWN alloy of some sort in your lathe. Roughly drill and/or bore a say 3/4 or one inch diameter hole into it using standard tooling to depth of an inch or so then use the D-bit as a boring bar. If it is well-sharpened, it should cut just fine as a boring bar.

I suppose there are those who are wondering why not just BUY a half inch reamer and be done with it. I think that would solve this particular job/problem. But then you have not yet unlocked the key to making a D-bit work. I think it is worth staying with it as being able to make a reamer of an off size on the spot is handy. Ordering one usually would take days and once you get the process down, a D-bit can be made from O-1 in less than 15 mins.

By the way, making it from O-1 (as opposed to HSS) allows one to use the lathe and mill to size and shape the D-bit prior to hardening. That is handy. I do have a surface grinder which is nice but not necessary to make a good reamer. In other threads I have mentioned anti-scale to be used in hardening O-1.

Denis


Denis

dazz said:

Hi
Attached are some photos.

The first version of the D-bit was very stubby to avoid too much grinding.
The modified version looks more conventional. What cannot be seen is that the shank is relieved from about 1/2inch from the D-section.

If the shank beyond the D-bit doesn't contribute to the way the tool works, then I guess one option is to reduce the shank diameter all the way up to the D-section.

Dazz

Click to expand...