D-bits

[bogstandard]

To save clogging up my post on making a spraymist unit, this part of which explains how to make one

http://madmodder.net/index.php?topic=2265.msg23824#msg23824

I asked if anyone would like to see my motley collection of D-bits, and a few said they would, so here they are.

These aren't all the ones I have made over the years, just a few good ones that I hung on to. These are the straight sided ones. To give some idea of scale, the bolt in the middle is 6mm by I think 30mm long.




These being the taper ones I have made. I never realised I had made so many over the years.




Now if you need to discuss D-bits, you have a post to do it in.


Bogs

[sbwhart]

Very artistic John

If you mounted them on a wooden board you could hang them on a wall.

 

Stew

[spuddevans]

Thanks for showing these Bogs 

Tim

[Russel]

In the spraymist thread I noticed that you prefer to harden but not temper the D-bit silver steel. What material will the D-bit work well machining? I know brass and aluminum are soft so they shouldn't be a problem, what about harder stuff?

[bogstandard]

Cast iron and free cutting mild steel is easy. I have used them to cut stainless, but not very often. When cutting stainless, they really need to be VERY sharp, plus I found it had to be done in one steady cut, otherwise the piece work hardens very quickly. It is the same, but not quite as bad, when cutting PB.

With reference to tempering. Just a personal view, but I seem to find I can get a much keener edge on the tool if I don't temper. I have never had one break on me yet.

As you can see in the pictures, you can make them in all shapes and sizes, and to resharpen, it is just a matter of relapping the flat face. If you are careful and not heavy handed, you can resharpen three or four times before the height split starts to become an issue.

John

[ozzie46]

  Thanks loads John.   

   Ron

[chuck foster]

nice little collection of d bit's john................thanks for sharing and reminding me how usefull they can be.

i remember making one to fix the tapered hub in a 55" dia. bronze boat propeller. i think the bore size was about 5" and the hole depth was around 12" and the taper was 3/4" per foot.
it took all day to make the d bit and bore out the propeller hub but it was worth it.

chuck 

[bogstandard]

You have hit it on the head Chuck.

D-bits can and will get you out of the crap, even when you are up to your neck in it.

People always try to go the most expensive and complicated route of reamers, whereas if I haven't got the right type or size of reamer in stock, I look at D-bits first. That usually solves my problem.

I am not saying that they are the be all and end all to the problems you will encounter, but they come very close to it.


John

[Russel]

This certainly opened my eyes! I've never even heard of a D-bit before this. Something new to try!

[NickG]

Next time I want a smooth, accurate round bore or a flat bottomed hole I will try this. Are they prone to chatter?

Nick

[bogstandard]

Nick,

I have never suffered with chatter when using D-bits, so I can't really comment.

I wouldn't think they would, as they are made minutely over half circle, and that alone would want to counteract chatter by holding the cutter in place.


John

[sbwhart]

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.

Cheers

Stew

[old-biker-uk]

I agree with Bogs, D-bit are great, here's a couple (1/8" & 3/16") I made yesterday to try pearling (the dome in the middle!) on my ornamental turning, 5 minutes with a couple of files.

I usually leave them dead hard unless I want a tougher edge, in which case I quench in cooking oil or a block of candle wax.
Note how cheap I am, using both ends of the silver steel....

Mark

[tinkerer]

The ornamental looks great. Did you do that on a mill? CNC?

[old-biker-uk]

Tinkerer - Did my first O/T with a dividing head on a small jig mill & liked the results so I built a Rose Engine.
Details here.

Mark

[Joachim Steinke]

Hallo,

oh yeah, D-Bits are a fine thing and sometimes a great alternative to the multiple cutting edge type cutters. Especially if you are in need of some tools which are hard to get from the ordinary suppliers, for instance special shapes and small dimensions, it really makes sense to grind your own cutters.

In former times I also made them from hardenable Carbon Steel (like 115CrV3 / 1.2210 or 45S20 / 1.0727), but since I have my Tool and Cutter Grinder I manufacture them more often directly from HSS or even carbide blanks.

Particularly if it comes to very small cutting faces and a little more durability for machining steel instead of brass or aluminium HSS or carbide is simply the better choice.

Here are two examples of a medium size and a very small dove tail cutter I made over the year. The “big” one has an effective diameter of 8.5mm, the small one cuts a 4mm diameter over the tips.








For very small diameters I normally use cylindrical blanks and will half the tip myself, but grinding this half away from a 10 or 12mm blank is a real ugly job without the opportunity of flooding the work with coolant. So I prefer pre-divided blanks for the bigger D-Bits as you can see on the photo.





And here at last one of the workpieces I needed the bigger one for, okay its only brass this time, but believe me, they will work fine in steel too.





There was no way to do the job on the table stops of the Mini Bonelle with my smallest commercial cutter (diameter 16mm). I simply had not enough room for a guiding bar wider than 11mm in front of the t-nut table, and the self made D-Bit does it very well.





And by the way, it can really make a lot of fun to realize your special jobs with, in principle, such simple home made tools.

By from Achim

[bogstandard]

Very nice indeed Achim.

I was going to mention that you can make your own milling cutters using D-bits, but you have shown perfectly how it is done, much better than I could have done.

Nice one.

Bogs

[Darren]

Very interesting, do the dovetail cutters cut the whole width of the slot at once or are they able to cut one side a time?

Doesn't brass and alloy look nice together 

[Joachim Steinke]

Hallo Darren,

this dovetail bits will work well either cutting at both sides at once or only at one shoulder of the profile. But cutting at both sides create less vibrations than the one sided operation, the cutting forces are in better balance and with only one cutting face on the tool this aspect becomes more important than on the commercial ones.

But naturally, as in fact with the multi faced cutters too, you have to make a central rectangular grove first to get the material out of the cutting channel. For good surface finish matched with precise dimensions I always take the last chips (if possible in a climbing cut) with only 0.05 to 0.1mm infeed. A convenient spindle speed is important too, for example the little 4mm router does not work well with only 2000 rpm ore so. As I have “tuned” my transmission I’m able to run the spindle at 5000 rpm, which creates the right speed range for such small tools.

And it’s always good to be a little bit careful on the feed rate at the beginning of the process. Especially (and obvious to all) the very small types are a bit fragile at the shaft constriction and not that “docile” at all, like the commercial ones. So you better start slow and approximate the feeding, depending on the feedback of cutting sound, vibrations and cutting force your work is “telling” you.

And YES…brass and alloy really look nice together!

As I have to do all the work on my little Proxxon FF400 miller, I still like to use Brass and Bronze on many components of low stress. Cutting steel is no real fun with such a weak machine. Okay, it’s possible and with adequate and sharp tools you can approach acceptable and precise results, as the fellows from the “Shirline Compartment” prove it every day with their perfect and masterly work.

But it really takes a lot of time and for me, being a real lazy boy, the need of cutting steel with greater dimensions always heightens the inhibition for starting new projects….ha ha ha…...

By from Achim

[Darren]

Thank you for the reply, there is a lot of information to be gleaned in there.

5,000 rpm, eek  I can see I'd have trouble with that on my mill  But I guess you need that because of the single tip cutter. Add more tips such as a commercial item and the speed can come down ...

You don't like steel much? Then you wouldn't like what I've been up to today 

[Russel]

This is a little off topic, but this thread has illustrated some of the values of a good tool grinder. I never really thought about how much it could expand your cutting tools.

Russ