What size drill

[HOWARDTParticipant @howardt]

You can always pass the tap through on a through hole.

Howard

Just looked at your photo again.

[JasonBModerator @jasonb]

Design needs more than one part in the blind threaded hole, if it were counterbored only the one at the end of the hole would be engaged in the thread.

 

Two bronze seats for a pump

This is the part that is threaded, its not a through hole but you can't see all of teh part in teh earlier photo

 

Edited By JasonB on 08/09/2016 20:48:39

[Ian PParticipant @ianp]

Posted by HOWARDT on 08/09/2016 20:30:18:

Question the design! Usually you would counterbore to reduce the thread length to keep it within design limits of the cutting tools.

Howard

Its all right questioning the design but what happens after questioning? If the item to be produced has to have a long internal thread to perform its function, then some method of achieving it has to be found. We would not get very far if tools could only be used within their limits.

I fail to see how a tap can cut in the reverse direction. I've cut threads to twice the tap length in soft materials and never experienced any cutting action when removing the tap.

Ian P

[HOWARDTParticipant @howardt]

Do both parts in the hole have to held by the thread? Without seeing the deisign it is difficult to comment.

Howard

[JasonBModerator @jasonb]

Yes

What I can't see is that if I stop the tap 1/2 a turn before teh cutting part enters the hole and wind it back out then it will be OK but you say that if I were to go 1/2 a turn beyond where the cutting part stopps it will overcut teh thread? Just don't see how 1 turn will make all that difference, have you got a link to the catalogue?

[HOWARDTParticipant @howardt]

We can all exceed design criteria, and we all do at times, if we get away with it then we are fortunate. But when things fail, as in the primary question we can only offer correct suggestions.

Howard

[Mike PooleParticipant @mikepoole82104]

Jobber drills are tapered towards the shank, I seem to remember a figure of about a thou per inch of length. The web also thickens towards the shank so a much sharpened or resharpened broken drill will have a large chisel point and require thinning. All my drills (mostly Dormer) measure undersized the same as Andrews. I find that if the finished size is important then double drilling will give a more accurate fit and can even be a bit tight. If freehand sharpening is used then it is very easy to cut oversize unless great care is used to keep the cutting edges the same length and the chisel point the correct angle.

Mike

[HOWARDTParticipant @howardt]

**LINK**

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 08/09/2016 20:05:13:

Posted by John Rudd on 08/09/2016 17:27:57:

Blunt tap?

That would be my guess too.

When I was a total beginner I often used 3.2 and/or 1/8" holes for M4 in brass and aluminium without breaking the tap. (Now I always use at least the recommended diameter drills: a broken tap jammed in the hole isn't worth the risk.)

Although delightfully cheap the tap I used with 3.2mm holes was new and sharp. I thought it was a bargain until I used it on mild steel. After tapping one hole it was hopelessly blunt.

Dave

Just like files, tools used on steel are never the same again when used on brass. Brass likes a sharp edge.

[Ian PParticipant @ianp]

Posted by Neil Wyatt on 08/09/2016 21:51:48:

Posted by SillyOldDuffer on 08/09/2016 20:05:13:

Posted by John Rudd on 08/09/2016 17:27:57:

Blunt tap?

That would be my guess too.

Just like files, tools used on steel are never the same again when used on brass. Brass likes a sharp edge.

Sharp yes but with zero rake.

Its not to bad drilling a hole from scratch but if increasing the size of an existing hole in brass make sure the cutting edges of the drill have been stoned flat to remove the rake (as if the drill had no twist).

I drill quite a lot of brass and have now gathered quite an assortment of drills that I keep for the purpose.

Ian P

[Enough!Participant @enough]

Posted by JasonB on 08/09/2016 20:24:24:

So whats one to do if you need a thread longer than the threaded part of a tap. The 1to 2 D is OK for fixings but what if teh thread is for something else like this one that was 90mm deep

You stop being so darned theoretical, do what you've done (and the rest of us do) and never notice the difference.

[JasonBModerator @jasonb]

Thanks for the link HowardT but I could not see it mentioned on that page is there a bit I'm missing or should I go to a particular section? I did look last night defopre you posted the link but could not see anything.

Also they all seem to be machine taps not hand taps that 99% of us use.

[Raymond AndersonParticipant @raymondanderson34407]

I have a lot of Emuge Franken taps and have had to thread deep holes on many an occasion never encountered a problem [ yet ] Probably the best taps available.

Jason,I think you are correct in that all Emuge Franken taps are " machine taps " I've never seen a hand one. I have the current paper catalogue here and can't find any hand taps in it.

cheers

[JasonBModerator @jasonb]

Just managed to find this pdf on taps, it seems their thread depths are based on clearing the swarf on high performance taps as far as I can see. Can't see the bit about going below the surface.

Looking at some of the details there I can see an M10 tap that has a 22mm length of teeth but can be used to cut upto 3xd which is 30mm so seems it is OK to run them below the surface. Also another M10 that only has 10mm length of cutting surface but can go to 2.5D which puts it 15mm below the surface!

As Bandersnatch says us hobby engineers tend to tap the hole first as we don't have much control of the diameter thread the tap will produce and then cut the male part which is easily adjusted to fit the female as required by adjusting the die or depth of cut when screw cutting on the lathe. We don't need it to fit another part from the other side of the world.

Those bronze seats being threadcut M18 x 1.0 with a test gauge cut using the same tap.

Edited By JasonB on 09/09/2016 08:21:23

Edited By JasonB on 09/09/2016 08:25:57

Edited By JasonB on 09/09/2016 08:35:45

[HopperParticipant @hopper]

Back in the real world, an often helpful habit when drilling then tapping is to place the taper tap into the drilled hole and look at how far it goes in before you start rotating it to cut the thread.

If the hole is the right size to give you 75 per cent thread depth, the taper tap should slide into the hole to the point where the teeth are 1/4 of full depth, as judge by eye.

If the tap will not slide very far in, say to the point where the root valleys are only just visible as tiny indents at the very beginning of the tap, drill out a size bigger until it goes in until the root valleys are a good 1/4 of the full thread depth at the point where the hole begins.

[julian atkinsParticipant @julianatkins58923]

I can categorically confirm that the shank size is often smaller than the twist bit OD. Not by more than a thou or two.

I regularly use drill shanks for certain precision purposes, and they often mike up smaller than the other end.

PS most of my stuff is Dormer.

Cheers,

Julian

[frank brownParticipant @frankbrown22225]

In the same way as you would not screw a bolt into a hole with chips in it, you don't unscrew a tap with chips behind the cutting bit*. As an Apprentice, one job We had was tapping out 4 Ba washers, 6" long "machine tap" (4"+ core diameter over top of cutting area) in the pillar drill, hold washer in pliars, push upwards on to tap, repeat until a pile of washers two inches thick was on tap. Then remove the tap and shake washers off. Repeat ad-nauseum.

* Turn metal upside down and shake chips out.

Frank

[stewart woodParticipant @stewartwood82335]

Good mouning, lots of free addvertising on here for DORMER DRILLS !! I worked for a drill manufacturer in sheffield ,we were a competiter to Dormer for many years , selling to the same custumers ,FORD and BL to name two plus all the other engineering supliers there were at the time . Not much to chose in quality of tools same machines and same staff because it was comon pratice to move from one to the other . Like most things today you only buy the name. Dormer are made in Mexsico now and Presto Tools in China . Tell you what though I bet Guring Drills are still made in Germany Stewart

[JasonBModerator @jasonb]

I thought the Dormer drills were made in Brazil, at least thats whats on mine and their taps in Sweeden.

Out of interest to the OP my 3.3mm Dormer A022 series measures 3.28mm at the end of the shank

[stewart woodParticipant @stewartwood82335]

May be , I looked on the web to find out were , the point is , its not here any more ,its the name you buy . As stated on here the shank will be smaller for clearance ,but when you get to the end of the flute the turnings wont be able to clear so in practice thats the depth to drill. Stewart

[Raymond AndersonParticipant @raymondanderson34407]

Stewart, as far as I know Guhring and Walter "Titex " are still made in Germany. I recently bought a new Titex 14.25mm Ø and it says " Germany " on the shank. It doesn't say Made in Germany just "Germany" These days it's well nigh impossible to be sure of where a product is made A lot of famous firms like to keep that part secret .

Edited By Raymond Anderson on 10/09/2016 08:44:00

[Raymond AndersonParticipant @raymondanderson34407]

Just been informed that a lot of Guhring gear is made in " Wisconsin " with the Metric and higher end gear still in Germany. Like I said you are never sure. Incidentally, all me Titex drills bore bang on size, and just measured the new 14.25 and it measures 14.21 at the end of the shank.

[KWILParticipant @kwil]

Nobody has mentioned that with straight fluted taps you have to be sure the chips are not packing the flutes. Wrong lubricant (or none) is another problem. Spiral fluted taps have much to recommend them.

Similarly, yes you can bore beyond the spiral depth of a drill, but common sense dictates that frequent withdrawal to clear swarf helps a lot!!

[HopperParticipant @hopper]

It is interesting to note too that the shanks of most drills beside being smaller diameter than the fluted section, are not made of HSS but of a softer, more flexible grade of steel welded on to the end of the HSS blank. You can easily turn the shank of a 3/4" drill bit down to fit in your 1/2" drill chuck if needed.

[Ian PParticipant @ianp]

Posted by Hopper on 10/09/2016 14:44:31:

It is interesting to note too that the shanks of most drills beside being smaller diameter than the fluted section, are not made of HSS but of a softer, more flexible grade of steel welded on to the end of the HSS blank. You can easily turn the shank of a 3/4" drill bit down to fit in your 1/2" drill chuck if needed.

I have turned shanks of large drills down, but I always assumed that the shank was a soft form of HSS.

Do you know that they are welded on extensions?

Ian

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