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Reamer size questions

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PANAGIOTIS EVRIPIOTIS27/11/2019 15:35:50
19 forum posts

Hello everyone,

New member here and I got some questions regarding reamers where you might be able to help me.

I am making some parts with imperial size reamers. The part has a hole of a 1/4 inch and 5/32. I want to achieve a tight fit for the parts that will fit into the hole and somebody suggested me to use undersized reamers by 0.001 inch.

Since it is quite hard for me to find in Greece undersized reamers, especially in inches I wanted to ask if anyone know any online shop or physical shops in London where I will be coming for a few days where I could buy undersized 1/4 and 5/32 inch reamers. I am only interested in chucking reamers preferably HSS (H7,H8 tolerances).

Thanks in advance for your help,


Sam Stones27/11/2019 18:37:58
798 forum posts
309 photos

Hi Panos,

You might like to consider an adjustable reamer (for the 1/4" at least). Not sure how small they go.

Would a tapered reamer (and therefore a tapered hole) work?




SteveI27/11/2019 18:42:19
247 forum posts
22 photos

not quite london but drill service in horley do (or at least have in the past) ground reamers to a specified size. I am a satisfied customer.

Derek Lane27/11/2019 19:28:52
392 forum posts
79 photos

I watched an u tube video where the presenter used either waterbase cutting lubricant or oil the first cut a tighter hole when reaming over the hole cut with oil, hope that makes sense. Will try to find it but I believe it was Stefan.


Edited By Derek Lane on 27/11/2019 19:30:02

Tim Stevens27/11/2019 20:12:56
1360 forum posts

It can be easier (sometimes) to size the hole with a standard reamer, and then make the internal part slightly oversize. This makes it much easier to find the reamer, and to adjust the internal part.

Hope this helps


lfoggy27/11/2019 20:29:49
150 forum posts
1 photos

There are lots of reamer tolerances but finding anything other than H7 is not easy. You could try Taylor & Jones of Sheffield. See last page of document below.....

Taylor & Jones

PANAGIOTIS EVRIPIOTIS27/11/2019 20:41:48
19 forum posts

Thank you all for your answers!


Tapered won't cut it in my case I think. I also considered the adjustable but in my knowledge there are no adjustable machine reamers, only hand ones. Theoretically I could buy and adjustable and do my job since I don't need to make a lot of these parts but I would like to search all the alternatives and as a last option resort to the adjustable hand reamer.


I will definetely check it out, I don't really care if it is in London if I can just order from them and they ship it to me.


I read about this somewhere else too but I don't how if I can get consistent results with that method. I will try it probably tomorrow and give an update.


I didn't mention this in the beginning because it is not an option. The shaft that goes into the hole is precision ground hardened stainless tool steel and I buy it already made since I don't have a lathe.


H7 is plenty enough, I will check out the document and ask.

If anybody else has and idea or a shop in mind please let me know. Although not that important I am also looking for 1/4 inch diameter precision ground hardened tool steel rod minimum 10cm in length.

Thanks again everyone for all your help

IanT27/11/2019 20:46:28
1800 forum posts
176 photos

Certainly agree with Tim - ream the hole and then make the part to fit it.

If I need a really (really) good fit, then I get the parts' OD as near as possible (to fit the hole) and then lap it to final fit. It's generally easier to make a simple external lap than a small internal one. Often not required but very handy when you do. Others here can probably turn down to microns - but I'm afraid I can't!

PS I do have a few adjustable reamers but I don't really use them very much - they are quite hard to set accuartely - very trial and error and too fiddly for me generally for "one-off" use...



JasonB27/11/2019 20:52:43
19881 forum posts
2167 photos
1 articles

You will have more luck finding 0.249" reamers listed on US sites. Not so hard to find 6.33mm reamers in the metric world. Rotagrip would probably post to you at a UK address, tighter tollerence but not much point in buying a one thou under reamer at H8 which would would be almost 0 to plus 1 thou.


Edited By JasonB on 27/11/2019 20:59:46

Andrew Johnston27/11/2019 21:23:58
5912 forum posts
663 photos

It's a question of finding the right tool shop. Some will stock a range of undersize reamers around an imperial value. One of my local tool warehouses stocks reamers in 0.01mm increments around common imperial and metric values. So when I wanted some imperial machine reamers for 1/4" I bought 6.35mm and for 3/8" I bought 9.53mm. For 1/2" I bought 1/2", as it was cheaper than a 12.7mm reamer!


Martin Hamilton 127/11/2019 21:44:45
185 forum posts

You can get something from They offer metric reamers going up in .01 mm increments, if you want 1 thou under .250" they have 6.33mm or 6.32mm. The 1 thou under 5/32" they offer 3.94mm or 3.93mm.

JohnF27/11/2019 21:51:42
1048 forum posts
158 photos

You don't say what the material is that you are going to ream ? It also would appear it may a stepped hole 1/4 leading to 5/32 ? Another point is on these diameters 0.001" interference is way too much .0005" would be more suitable.

Tim is really correct with good engineering practice however you say this is not possible, It depends on how many holes you have to do but another option is to "stone" down a standard reamer - difficult if the hole is very deep and you are using the full length of the reamer. but it can be done using a jig. Not the best way but sometimes needs must to get the job done.

Another trick is to "condition" a new reamer by running it through cast iron several times, this will generally make it cut smaller by a few tenths - may not be enough so you would still need to resort to running a fine stone against it with VERY low pressure. For the CI drill the hole 1/64 under then ream.


Andrew Johnston27/11/2019 22:15:13
5912 forum posts
663 photos
Posted by Martin Hamilton 1 on 27/11/2019 21:44:45:

You can get something from They offer metric reamers going up in .01 mm increments,

I'm glad you posted that. I was going to say that my local tool emporium stocked reamers by 0.01mm as that is what I remembered. But I thought some smartypants would rubbish the idea. So I didn't!


Martin Hamilton 127/11/2019 23:38:05
185 forum posts

A lot of the Toolex reamers go up in .005mm increments as well.

JA28/11/2019 00:09:49
1096 forum posts
58 photos
Posted by Martin Hamilton 1 on 27/11/2019 21:44:45:

You can get something from They offer metric reamers going up in .01 mm increments, if you want 1 thou under .250" they have 6.33mm or 6.32mm. The 1 thou under 5/32" they offer 3.94mm or 3.93mm.

Thank you.

(and they are local)!


Hopper28/11/2019 01:35:24
5137 forum posts
114 photos
Posted by PANAGIOTIS EVRIPIOTIS on 27/11/2019 20:41:48:

If anybody else has and idea or a shop in mind please let me know. Although not that important I am also looking for 1/4 inch diameter precision ground hardened tool steel rod minimum 10cm in length.

Thanks again everyone for all your help

If you search for steel dowel pins you might find something. Maybe not that long though. Can the design be changed to use standard sized steel dowel pins? You can also get dowel pin reamers that are made in two sizes, one for an interference fit and one for a sliding fit. No idea where you buy them as I only ever used them at work.

I.M. OUTAHERE28/11/2019 02:18:59
1468 forum posts
3 photos

I bought a set of over and under reamers 1/8 to 1/2 and they are supposed to cut .001 inch under and .001 over - more like on on size and .002 over ! This will probably get better with use or at least i hope so !

Is it possible for you to make and use a toolmakers reamer ?

When everything else fails Loctite prevails ! I”m sure there is an advertising slogan in there somewhere 😀

PANAGIOTIS EVRIPIOTIS28/11/2019 08:04:20
19 forum posts


As I said it the shaft that goes in the hole is of fixed size so I can't go with Tim's method for now.

Regarding the adjustable reamer, if I need it only for this hole and set it up by trial and error as you said then theoretically I can leave it like this and use it only for reaming that hole for a tight fit right?


That was my solution in the beginning and I contacted mcmaster carr in the US and they told me that they will not accept my orders due to US export regulations which is very strange.


I will be more descriptive. So I am mainly drilling and rimming 6al4v titanium and stainless tool steel. both of them have a 1/4 hole and another 5/32 hole. Each hole is for a different part. The thickness I am drilling is 1.5mm to 5mm max.

Right now I am using a carbide reamer and I am guessing that your ideas refer to an HSS reamer. Can you give me some info or resource regarding stoning a reamer and about the jig that you are referring to?


The design with my current set up is not possible to be changed to metric unfortunately because I am buying some parts from the US which I can't make yet. I will check out the dowel pins. I was also considering of going to a machining shop in my area and ask that they make me one but I am not that sure of the accuracy that they can achieve.


I didn't know anything about toolmaker's reamers, theoretically they would work but I am guessing I will need to find someone to make them.


To sum up, to achieve the tight fit I need on the aforementioned materials I can only mess with the hole and not the shafts. I cannot buy undersized reamers from the US because of some stupid reason about regulations so my only option is to get something from the UK if I can find.

If I can't find that then other ways are to get an adjustable reamer and by trial and error set it up ones and keep it that way. Or I can buy HSS reamer stone it or run it through cast iron. Lastly I will contact the shop mentioned about sizes.

JasonB28/11/2019 13:17:45
19881 forum posts
2167 photos
1 articles

Look at my post above and click on the bold "Rotagrip" this will take you to a 6.33mm reamer which is equal to 0.2492" so the size you need.

There are many others that also sell similar sized metric reamers as all the posts after mine show.

Edited By JasonB on 28/11/2019 13:17:59

PANAGIOTIS EVRIPIOTIS28/11/2019 14:03:37
19 forum posts


I have bought from Rotagrip before through ebay. I checked your link already but the problem is that I do not have a good grasp of tolerances yet so I can't really judge how smaller does the reamer have to be in order to get a tight fit for a 0.250 hole. Maybe you or any of the others can advice as to how lower I should go to get that tight fit.

Also for anyone who might be interested I contacted drill service as mentioned above and they can make a 0.249 and 0.1560 reamer but they sell at 45 and 40 pounds respectively and that is for HSS reamers. It is quite a high price I think

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