Angled d-bit / machinist reamer?

[FulmenParticipant @fulmen]

I’m trying to find a bit of info on homemade reamers. Specifically I need a precise 3mm hole in brass, and I do have some 3mm silver steel. Isn’t it possible to use a rod cut at an angle as a diy reamer? I’ve tried googling for this but I’m struggling to find any good sources. Maybe I’m using the wrong term?

[JasonBModerator @jasonb]

I have done it in the past. Cut at about 20deg so you have a long slanting cut surface. Harden and then rub on a stone or diamond slip to get a nice crisp edge and feed it into a slightly undersized hole at slow speed or turning by hand.

[Roger BParticipant @rogerb61624]

I know these as toolmakers reamers and like Jason have used them in special cases. The angled type seem easier than trying to get the flat ‘exactly’ on the centre line as in a D bit.

[FulmenParticipant @fulmen]

Yup, that’s what I’m talking about. I just tried making one and eyeballed the angle to 25°. I’m sure it’s going to cut, but there must be some page discussing these in more detail somewhere, right?

[Andy StopfordParticipant @andystopford50521]

There isn’t much to add to what Jason said, watch out for the tip curling over during the hardening process, stone it off if it does.

They work well, but tend to make the hole over-size (though that may just be operator error).

[Roger BParticipant @rogerb61624]

Reamers will produce oversize and tapered holes unless they are allowed the freedom of a floating reamer holder or the tailstock is aligned to better than one tenth of the precision required.

[FulmenParticipant @fulmen]

Well of course it’s not going to be perfect, I’m not expecting or demanding miracles. And it needs to be a little bit oversized as the hole if for a pin from the same stock and needs to be a sliding fit.

“Toolmakers reamer” did return a few useful hits, but nothing really comprehensive.

https://www.hobby-machinist.com/threads/toolmakers-reamer.100016/
https://www.practicalmachinist.com/forum/threads/how-do-you-make-a-d-bit.225698/#post1576353
https://www.homemodelenginemachinist.com/threads/diy-reamers.4142/

 

The last link provided this image, and the #2 looks interesting but I can’t really see exactly how the relief is placed.

[JasonBModerator @jasonb]

If you make your reamer on the end of a 330mm length of silver steel there will be enough flex in the 3mm dia for it to align itself, floating or not.

Most commonly available reamers being H7 or H8 are a plus size tolerance so I would expect them to be over nominal.

[John HaineParticipant @johnhaine32865]

IIRC I read about these in one of Lautard’s books where he calls them whistle reamers. I think also he recommended stoning a small relief on the back of the point to guide it into the hole. I have made one but can’t remember what for or if it worked – I think it must have done since it’s still in the drawer, wasn’t chucked in the scrap bin in disgust!

[BazyleParticipant @bazyle]

After thinking a bit about this I am attempting to analyse how it works. Lets assume the flat face is upwards in case it aids the description of operation. The flat face width starts small increases to the rod diameter and then decreases, with that peak being at half way up.
As the reamer enters the hole the tip is not cutting just guiding and as the hole is undersize the reamer is being pushed upwards. It starts to cut as the width of the flat face matches the undersize hole diameter not at its max design width -almost- but because it is pushed upwards it is contacting above centreline and therefore narrower width. Also the cutting edge has negative rake.
Even though the hole is being enlarged the tool remains above centreline because the tip is still resting in the pilot hole and therefore the bottom of the tool is in mid air. At some point the full width section has to get into the hole despite the tip still being above centreline.

At this point my imagination is getting a bit strained about what happens. It does however explain why some people suggest boring the start section of a hole to be reamed.

[FulmenParticipant @fulmen]

After making the reamer I discovered that I didn’t have any bits between 2.5 and 3mm. I tried with the 2.5mm, and while it had no problems cutting the hole it came out around 3.2mm and tapered. But with a fresh 2.9 bit it worked like a charm with good fit and finish.

[Fulmen]

On Fulmen Said:

[…]

https://www.homemodelenginemachinist.com/threads/diy-reamers.4142/

 

The last link provided this image, and the #2 looks interesting but I can’t really see exactly how the relief is placed.

#1 is what my Dad used to make

But I do agree, #2 looks interesting.

MichaelG.

[FulmenParticipant @fulmen]

I made it like #2 (hopefully), just adding a bit of taper and back relief to the cutting edge.

[FulmenParticipant @fulmen]

I don’t have the bit for a photo but here’s a 3D rendering:

https://www.model-engineer.co.uk/members/fulmen/mediapress/miscellaneous-stuff/2026-10-14_214816/

[TendorParticipant @tendor]

This 1/4″ silver steel reamer worked well for me. The chips formed are on the cutting edge.

[TendorParticipant @tendor]

A brief reference is made in L.H. Sparey’s The Amateur’s Lathe, page 89 and figure 81.

[FulmenParticipant @fulmen]

@Tendor: Like this?

[TendorParticipant @tendor]

No. Without the flats on the leading flanks. Just an oblique flat surface.

Like #1 in the sketches. But it did have the weak point reduced with a bit of a taper before the oblique cut was made. I don’t think that affected its operation.

[FulmenParticipant @fulmen]

I see. I’m still trying to figure out #2 and was hoping you had the answer. Either way the first render was what I used and it worked fine with a proper sized starter hole.

And here is the info from “the amateur lathe”, made available here

https://archive.org/details/amateurslathe0000spar/:

Is it just a chamfer?

[Michael GilliganParticipant @michaelgilligan61133]

Looks that way to me … and [dare I say] rather pointless

MichaelG.

[Martin Johnson 1Participant @martinjohnson1]

I think that picture is the Type 2 shown in earlier diagram.  I have made them generally as the above phtoto but a bit more rounded off.  It helps the pointy bit find the drilled hole without bouncing off the adge and shifting the work as would Type 1 in theory.  Also lets you ream right through with a shorter reamer – remember the full diameter section is some way back from the end on Type 1.

Martin

[duncan webster 1Participant @duncanwebster1]

The handwritten blurb on Fulmen’s post suggests 1 thou interference pet 1/8″ diameter for press fits. This seems very high to me. Interweb suggests H7/s6 which gives 1 to 3 thou per inch if I’ve read the table correctly.

[jaCK HobsonParticipant @jackhobson50760]

I tried these to ream out a hole in a stainless steel bolt. Didn’t seem to work very well on stainless – tend to jam.

I found a way of making an ‘adjustable’ reamer. Sand silver steel so it is very slightly undersize. Cut a slot. Raise a burr by rubbing a burnisher along the ‘cutting’ edge (burnisher can be anything hard). Harden etc. It is very hit and miss as it depends on the pre-sanding, raising burr, heat treat changes sizes – but I got there in the end. More bodging than engineering but that suits me! I only used on softer materials.

 

[FulmenParticipant @fulmen]

So, like this then?

This is a 20° included chamfer and a 20° oblique. And I think it’s a sensible idea, it should move the cutting action closer to the center line.

[bernard towersParticipant @bernardtowers37738]

jack, stainless bolt material can be very unforgiving, if it hasnt got A2 on the head give up.

[Author]

Posts