A question about reamers and hole tolerances.

I want to make a bushing with a 7mm hole specifically to H7 tolerance. I had a look for a suitable reamer and came across offerings from sourcingmap on Amazon which have the merits of being cheap and being on next day delivery. However I can't understand the table of technical info:

I can't reconcile this with info from other sources which all tell me that 7mm H7 should be between 7.000 and 7.015mm. For example, the entry for 6.5 - 13mm above suggests that for a 7mm mm reamer D will be between 7.000 and 7.005 mm and the H7 column gives a tolerance of +0/-0.027mm. Which seems to suggest the reamer might actually cut under size. Am I misunderstanding the table?

Perhaps I should steer clear and buy elsewhere ( think I probably will actually, ARC's offerings are only a few quid more and they deliver pretty quickly) but I'd like to know what the table above means. If anyone can elucidate I'd be grateful.

Robin

Methinks they've ptobably got the sign wrong on H7 and H8. Other than that, the values seem close to the standard. Having said that, I've got no idea what a D4 tolerance is.

Mark

As I understand it D is for tap pitch diameter tolerances. Usually slighty greater than the corresponding H number, Always +, larger than nominal.

How that relates to reamers I don't know.

Clive

I looked up reaming tolerances in a PDF from Phantom (Don't know how to upload this PDF).

For a 7 mm hole H7 you should use their 7.01mm precision reamer. They don't spec the tolerances, just the reamer size to select.

D8..D12 are also tolerances, couldn't find D4.

If you really need H7 then you should buy a quality tool and use the advised hole drill diameter.

I have reamers from HBM (Netherlands) and most of them are way (+0.03 mm) out of spec.

Apart from anything else, what is the service available from these Am a zon suppliers - compared to a good model engineering supplier?

How many users actually use these devices in the optimum manner (to achieve the expected tolerance)?

Cheapness is not always a merit. Think here whether a commercial user/buyer would even consider these cheap buys.

Can’t throw any more light on the table unfortunately. But in the past life I used to specify cutting tools for high volume production, all tools were specified to produce the required size, a proportion of the drawing tolerance. The actual tool size was normally towards the top end of the tolerance to allow for wear and regrinding. Reamers are available in at least two tolerances to produce either H7 or plus size holes, also dependant on material being cut.

As has been said make the parts to suit unless it is for someone else who specifies the size on a drawing.

I wonder if these figures are aimed at the American market which uses a shaft based system rather than our Hole based system. That would also tie in with the 6.5 to 13 range being close to 1/4-1/2" but if you look at say Zeuz that is 6-10 and 10-18 ranges.

The ARC ones work for me and I have bought all the common size machine reamers and now seldom use my collection of hand reamers built up over a number of years. Will still depend on pilot hole size, material, wet or dry cut and obviously the actual size of your shaft rather than nominal.

Edited By JasonB on 16/05/2022 08:00:45

and if you ream as a single pass or a double pass.

regards Martin

I have never used Amazon for anything other than books and, for what it is worth, no longer use the model engineering suppliers for reamers, milling cutters etc.

The industrial suppliers are quite happy to take your money, are no more expensive and usually give a next day service. I can recommend, just as a satisfied customer, Drill Service (Horley) Ltd.

JA

Floating Reamer holder as well!!!

The H7 column doesn't look right to me either - looks like over a thou interference would be within limits on a 7mm shaft!

I tend to go by the limits and fits shown in the Zeus booklet.

And I don't know if I'd buy from a supplier who thinks Glass-Hard Steel is anywhere near 40 HRc... (?! )

You ought to! I wouldn’t! I steer well clear of suppliers like that.

Totally agree with JA, buy from an industrial supplier, they cannot risk their reputation supplying rubbish to the professionals, I have been using Drill Service for many years and can recommend them, no connection with the company only a satisfied customer.

Thanks for replies. I'm actually happy that nobody has been able to explain the table in my opening post. Not having an engineering background I've had many 'Oh gawd, here's another mysterious thing I have to understand' episodes and I thought this might be another. Seems not - the table is just wrong, even allowing for sign changes.

Mick - thanks for pointing out the 40HRC /Glass hard thing, I hadn't noticed that because (apart from difficulties with the numbers) I couldn't really understand the layout of the table. I can cope with 2-D ISO tables!

I have ordered a reamer form ARC, which whilst not 'industrial' will doubtless be more trustworthy than the Amazon offerering.

Comments about the importance of technique and ancillary kit (floating holder) made me realise that even if were to spring £40 or so for a Guhring or Dormer I still wouldn't be guaranteed H7 tolerance. Doh! Well I'm here (primarily) to learn and the comments made me think, so thanks.

The job is one of those 'help someone out' things which crop up from time to time. The 'client' has now agreed to send me the broken bushing so I'll be able to make an accurate copy without worrying about standards. It's been an educational thread for me though.

Robin.

ARC actually have quite a large commercial customer base, obviously not for the machines but cutting tools etc do also go to business and further education, etc

If you look closely at the table there is actually a - behind the 40HRC suggesting steels over 40HRC and the box to the left has -40HRC which would be steels under 40HRC not that Glass hard steel is 40 HRC

The bottom line of the chart shows which of the two reamers is better suited to each material. Above that to the left the HSS reamer has a circle and the Carbide reamer has a triangle. So they are suggesting the carbide reamer for the hard steels & stainless and the HSS one for the easier cutting steels, CI, Aluminium and copper. 

Edited By JasonB on 17/05/2022 07:54:04

So what's wrong with '>' if you think think they mean 'greater than'?

Or in the case of glass-hard steel it ought to be '>>' -  'a lot greater than'.

What you're suggesting is that the table author's familiar with materials symbology some of us would consider arcane, but doesn't know basic mathematical symbology of the sort any secondary-school pupil would be familiar with?

And they can't spell 'chucking' either.

P-lease...!

Edited By Mick B1 on 17/05/2022 09:00:59

After a bit more research I think I can confirm that D tolerances primarily refer to the pitch diameter of metric taps. Presumably to avoid confusion with H tolerances which, strictly, were intended for holes.

I gather American practice is supposed to be to use GH rather than H for tap pitch diameter tolerance but this seems to be honoured more in the breach than observance.

For practical purposes it appears that D tolerances pretty much follow H tolerances with the same number.

I was unable to find a simple, straightforward explanation on the internet. the more detailed and potentially useful the presentation the more [deliberately?] confusing the explanation.

This link from Guhring **LINK**

https://www.guhring.com/media/InteractiveCatalog/jkko1oebbiy/files/basic-html/page32.html

has one of the less confusing presentations on the second page! I advise having headache pills, or at least a wet towel, handy before reading.

It all begs the question as to what a D4 tolerance has to do with reamers.

The Guhring reference above states that each D limit = 0.013 mm followed by a couple of examples that seem to make no mathematical sense at all.

Clive

I think the above table is a load of rubbish. It is interesting that copper is included. At work we broke over 60 1/2" reamers trying to ream holes in a copper block. We gave up and the research project was abandoned.

This is the table I use:

and the associated fits are:

A large D does not appear in either table. Given that reamers are usually H7 you can decide on the shaft diameter.

For completeness I include a third chart:

I do try to work to the above tables.

JA

Looking again at Robin's chart I think the "D" in the right hand column is a typo.

Edited By JA on 17/05/2022 17:02:37

We spent thousands of pounds of your, the tax payer's, money on that project.

I note that your profile says nothing about your experience.

JA