# TAP PROBLEM



## riversidedan (Jul 6, 2021)

so we gotta 3/8 bolt with SAE threads , the chart sez to drill the part with 5/16 drill then tap with a 3/8 16 tap.........
the pitch gauge reads 16 and lines up with the tap and bolt  but when I go to tap doesnt wanna go in........cant figure it out


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## hman (Jul 6, 2021)

I may be a bit rusty on this ... but I've always thought that SAE thread pitches were equivalent to NF (national fine) threads.  The NF thread pitch for 3/8" is 24 TPI, not 16 TPI (which is NC, equivalent to the old USS standard).  But then, you did check both the bolt and the tap against the same gauge, and tapped according to the chart.  Guess I'm stumped.

OK, silly question ... might the bolt be left-hand threaded????


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## Ken226 (Jul 6, 2021)

riversidedan said:


> so we gotta 3/8 bolt with SAE threads , the chart sez to drill the part with 5/16 drill then tap with a 3/8 16 tap.........
> the bolt gauge reads 16 and lines up with the tap and bolt  but when I go to tap doesnt wanna go in........cant figure it out



What kind of tap are you using?  As in brand and material?   

What type of material are you tapping?  With aluminum you can get away with poor taps.   With tougher steels,  not so much.


If your already using a quality HSS tap, disregard the following info.


 When I first started tapping holes, I bought cheap carbon steel tap sets from local auto parts stores.  

Not one of them, ever worked very well in steel  and in some cases, tougher steels like 4150 or in titanium,  the hole would remove the teeth on the tap.

If you haven't already, try a HSS tap.  Something like this:






						Amazon.com: MaxTool 3/8-16 Spiral Point Taps HSS M2 Thread Taps 16 TPI FULLY GROUND RIGHT HAND; SPF02W01R24 : Industrial & Scientific
					

Buy MaxTool 3/8-16 Spiral Point Taps HSS M2 Thread Taps 16 TPI FULLY GROUND RIGHT HAND; SPF02W01R24: Spiral Flute Taps - Amazon.com ✓ FREE DELIVERY possible on eligible purchases



					www.amazon.com


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## projectnut (Jul 6, 2021)

Is it possibly a tapered tap rather than a plug tap?  If you're using it for a blind hole it may not be cutting full threads at the end.  A taper tap usually has between 7 and 10 chamfered threads at the lead end.  That could be over 1/2" on a 3/8-16 hole.  They're great for starting a threaded hole, but should be followed by a plug tap (3-5 chamfered threads) on through holes, or a bottoming tap (1-2 chamfered threads) on blind holes.


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## SLK001 (Jul 6, 2021)

My guess is that you're using the wrong tap to start your hole.  A bottoming or plug tap is to finish a hole (blind), while a tapered tap starts a hole (and can be used for the entire hole, if it is a thru hole).  Although there are more types of taps, the usual progression of a tapped hole is start with a taper tap, then move to a plug tap, then move to a bottoming tap.  In most materials, you can skip the plug tap and go from taper to bottoming tap.


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## Karl_T (Jul 6, 2021)

most cetainly you have either the wrong or a poor quality tap. A picture would tell the story.


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## RJSakowski (Jul 6, 2021)

If the tap won't start in the hole, it is most likely due to either the wring style tap or a bad tap. as stated above.  Taps sold at DIY and auto parts stores are usually plug taps.  One get-around us to drill the start of the hole just slightly smaller than the thread o.d. for a few threads which will allow the tap to get a bite and draw itself in.  This isn't possible in all circumstances though.  Another is to tap with a drill press or lathe  with the quill providing pressure to push the tap to get it started.  These are Band-aids though and the proper procedure is to get the proper tap.


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## markba633csi (Jul 6, 2021)

5/16" is the correct size tap drill for 3/8"-16 threads so the tap must be the culprit.  Remember you have to push a bit to get the tap started, chamfering the hole helps. And you have to check carefully that the tap is started straight as you begin cutting- past a certain point you won't be able to correct the tilt if it gets started crooked
Forward, back, forward, back, forward, back is the motion you want to use when hand tapping
-Mark


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## projectnut (Jul 6, 2021)

My apologies for my first post.  I misread the original post thinking the bolt wouldn't go in the threaded hole.  I see after reading it a second time the tap won't go in the drilled hole.  I'm wondering if you have a roll form tap rather than a thread cutting tap.  Roll form taps usually have the designation RF on the shank.  

A 3/8-16 roll form tap requires an 8.8mm (.346") drilled hole while a 3/8-16 thread cutting tap requires a .312" (5/16") drilled hole.  The roll form tap in this case needs a hole .034" larger than one for a thread cutting tap.


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## Richard King 2 (Jul 6, 2021)

If I were you I would measure and look at everything again.  Measure twice and cut once as the old saying states. How did you drill the hole, on a machine or by hand?  If it is cockeyed it may not start.  When I was an Apprentice I  made a Tapping block . so I could keep the tap straight when I ran it into the hole.  Also the members above all make some good points.   If your new to the trade, buy only Industrial Grade drills and taps from an Industrial supply.  I would stay away from imported ones.  If a tap breaks, you will play heck getting it out.  Also use tapping fluid.  Buy a starting tap, a plug tap and a bottom tap and practice.  Another thing you can do is to drill the hole one letter or size bigger if the final tapped hole does not support weight.  I do this a lot when I install way wipers   If nothing helps please show us some photo's.  Good luck

PS:  Look at the tap and look for letters RT meaning right hand.  If it says LF that's the problem


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## pacifica (Jul 6, 2021)

riversidedan said:


> so we gotta 3/8 bolt with SAE threads , the chart sez to drill the part with 5/16 drill then tap with a 3/8 16 tap.........
> the pitch gauge reads 16 and lines up with the tap and bolt  but when I go to tap doesnt wanna go in........cant figure it out


If your drilling is particularly accurate you may try larger than 5/16"(77 % thread), letter O is .3160 at 72 % thread. I do this in hard to tap materials
all the  time, going as low as 50% thread engagement. And this is using low run out drills in a mill with high quality taps. The first 3 threads hold over 90% of the load . According to *Regal Cutting  Tools, increasing the thread engagement from 60% to 72% in 1020 steel reguires twice the torque but increases strength by only 5%.*


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## riversidedan (Jul 6, 2021)

am wanting to tap into some simple 6061 ...here you see the  3/8 bolt  thread gauge and  3/8 16 tap

BTW Ive had good luck with previous tapping adventurers this one thru me a curve

I also put the tap in the drill chuck on the lathe turning the chuck by hand but the tap woudlnt start cutting.... while looking at the tap , the 1st 3 rows are flat and not sharp from the top on down so Im thinking the tap is garbage and the wrong shape

in the 2nd pic the 1st 3 cutting edges are flat not sharp like the rest are on down, so again am thinking thats the culprit


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## SLK001 (Jul 6, 2021)

The tap you show is a plug tap.  To start a thread with that tap will require a considerable amount of force.  Get a taper, or starter tap.


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## riversidedan (Jul 6, 2021)

thats what I was kinda thinking but didnt have a taper one in the lot...........am also assuming the 5/16 drill should be the right one for that size tap. correct me if Im wrong


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## hman (Jul 6, 2021)

Looks like I misunderstood your post when I first answered.  5/16" is indeed the correct drill size for tapping 3/8-16, especially for aluminum.  Sometimes you want to go a skosh larger if tapping something tougher, like steel.  Guess I'll second the opinion of other posters and suggest a good quality (ie, HSS) taper tap to start with.  You can also try slightly beveling the outer edge of the hole with a countersink.  

I myself like using name brand "spiral point" taps for all my tapping.  These are generally only available in "plug" style, but have worked well for me in steel, aluminum, plastic, etc.


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## epanzella (Jul 6, 2021)

I had a similar experience.  Despite all factors correct the tap required so much force it would have broken if I continued. Went in the drawer and got a high quality HSS tap and it went right in.


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## Richard King 2 (Jul 6, 2021)

Buy a new tap.  That tap looks like it's dull  and as SLK said, that's a plug tap.   Practice some power tapping on some scrap.


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## riversidedan (Jul 6, 2021)

what is your guys thoughts about Irwin taps?


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## Richard King 2 (Jul 6, 2021)

I googled Irwin Tap reviews and they are a 4 1/2 out of 5 stars.  Looks like they can be bought at hardware stores.  I order my taps from Viking Drill in St Paul, MN where they are made.     http://vikingdrill.com/viking-Tap-Troubleshooting.php


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## projectnut (Jul 6, 2021)

That doesn't look like a plug tap to me.  Rather it appears to be a bottoming tap.  A plug tap has 5 to 7 chamfered threads on the leading end.  A taper or starter tap has 7 to 10 tapered threads on the leading end, and a bottoming tap has 1 to 2 chamfered threads on the leading end.

This tap appears to have only a single chamfered thread at the leading end, and is consistent with a bottoming tap.  If you're tapping 6061 aluminum a plug tap should be easy to start and is all that's needed if you're doing a through hole.  If you're doing a blind hole the plug tap should be followed by the bottoming tap to get threads to the bottom of the hole.

I don't know who's rating Irwin taps at  at 4 1/2 out of 5 stars.  They are almost always carbon steel and made in China.  They might be good for a couple holes in aluminum, but that's about it.  In the professional world they are rated as one step below junk.  Go with HSS taps from name brand manufacturers like Morse, Brubaker, Triumph, Precision, Regal, YG 1, Viking, Hertel, Dormer, Sandvik, Union Butterfield, Kennametal, Guhring, or any of a hundred other name brands offered by industrial suppliers.


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## markba633csi (Jul 6, 2021)

You forgot the excellent Widia/GTD taps- the gold standard, for me anyhow


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## 682bear (Jul 6, 2021)

There are 3/8-16 HSS taps on ebay... for less than $10 shipped...

Why fool with carbon steel taps at all?

-Bear


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## Larry$ (Jul 7, 2021)

riversidedan said:


> what is your guys thoughts about Irwin taps?


Chances are they are less than ideal taps if they are sold in hardware or big box stores. Quality taps are "too" expensive for the people that go to the hardware/big box stores. The cheap taps get really expensive when you break them in a hole. If you can't use a drill press or mill, just drill a block of hardwood by hand or better on a drill press and use it to keep the drill & tap at 90 degrees. Center punch so the drill doesn't wonder off the the bar while you aren't looking. The tap you are trying to use doesn't have enough starting threads.


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## Eddyde (Jul 7, 2021)

For hand tapping a few holes in aluminum, the Irwin tap will work just fine.


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## Ken226 (Jul 7, 2021)

riversidedan said:


> what is your guys thoughts about Irwin taps?




The reason everyone keeps telling you to get HSS taps  and skip that carbon steel stuff is because they've learned, from experience.   

Most everyone here has, at some point, needed to tap a bunch of holes at some point in their careers.    Most tried carbon steel taps,  learned the lesson, and moved on.

This HSS thing they keep mentioning, is the most important aspect.   Not the brand so much.   

You have, here, for free, the collective experience of a whole lot of people,  who have been exactly where you are,  found the solution, and are now offering the benefit of that costly experience.

Get a HSS tap.  You'll soon find yourself on here responding to a similar thread,  telling others the same thing.

But yes,  the Irwin tap will probably be fine for aluminum.  Personally,  I like my taps to be good for steel too.   I've used Irwin taps, in both aluminum and steel.  Got a few good uses out of it.    My HSS taps last year's, and make tapping holes an easy thing.  

When I first started out, using hardware store taps made the experience suck.  I was always worried about breaking taps, and many times did.  Sometimes, even in aluminum.   




     With HSS, I can power tap  several hundred holes with my mill and never have an issue.   
     A couple years ago I did a run of about a thousand 6061-t6 14mm, 17mm and 5/8" speed handles to fit import, and Glacern 5" milling vises.    I set up a work stop on my PM935 and each one got a 5/16-18 hole.   All done with the same 10$ hss tap.  It took less than 5 seconds per hole.  I still use that same tap.





One of my customers at the time was Jesse James Gunsmithing LTD.


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## lesrhorer (Jul 7, 2021)

markba633csi said:


> 5/16" is the correct size tap drill for 3/8"-16 threads so the tap must be the culprit.


That is not quite accurate.  In general, the tap hole should vary with the type of material being tapped.  The thread depth can vary from as low as 25% to a maximum of something a bit less than 100%.  Typically, the harder the material, the lower the thread depth.  Thread depths less than 50% or more than 75% are usually only for very special situations.  A 5/16 drill will produce about a 75% thread depth, which is good for plastics, brass, aluminum, etc.  It is a little bit small for hard materials such as mild steel, stainless steel, etc.  It is probably OK for cast iron, although one might consider going to perhaps about 0.32" or so - about a P drill  - if one is having trouble in cast iron.


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## lesrhorer (Jul 7, 2021)

Ken226 said:


> The reason everyone keeps telling you to get HSS taps  and skip that carbon steel stuff is because they've learned, from experience.



Amen.  Most of us are concerned about cost, and high carbon steel is almost always less expensive up front than HSS.  Believe me, I can sympathize.  In the long run, however, HSS is going to wind up less expensive, because it will cut faster and cleaner and usually last much longer.  As others have mentioned, the less expensive taps will work well enough if all you are machining is brass, aluminum, plastic, etc.  Otherwise, HSS taps are pretty much well worth the cost.  The only exceptions, perhaps, might be a specialty tap, which is only probbably going to be used once or twice in a blue moon, or a sacrifice tap, which one knows will be destroyed by the tapping process, or a bottom tap.

Personally, rather than buying bottom taps, I would recommend  buying HSS plug taps, and along side them buy cheaper plug taps and grinding the tips off.  After making the initial thread with the HSS tap, the modified carbon steel tap can be used to finish out the hole.  The bottom tap will only be cutting three or four threads, in each hole, and when it gets dull, it can be sharpened several times by grinding back the tip.


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## lesrhorer (Jul 7, 2021)

When hand tapping, if practical, I like to counter-bore the hole a bit.  This not only helps a lot in getting the thread started, it also helps make sure the tap is straight.  I also heartily recommend a tap guide.  They are inexpensive, and really help a lot with preventing tap breakage and with getting better quality threads.


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## projectnut (Jul 7, 2021)

markba633csi said:


> You forgot the excellent Widia/GTD taps- the gold standard, for me anyhow


Sorry about that.  I knew I would miss at least 1 quality brand.  Rather than work from memory I should have taken a few steps into the shop and looked in the tap cabinets.  I probably have well over a hundred WIDA taps in different sizes and configurations.

I must admit I do have a few carbon steel taps in the mix.  Right now I think it's limited to 3.  I can't even remember the job I bought them for, but it was a 1 off and probably close to 20 years ago.  They're 9/16-20 left hand thread.  I searched high and low to find them, and finally found a set (Taper, Plug, & Bottom) at McMaster.  At the time they cost around $40.00 for the set.  McMaster doesn't even carry that size in carbon steel anymore.  The only 9/16-20 left hand tap set the currently have in the lineup is HSS, and it's almost $220.00 for the set.

In most cases I don't believe carbon steel taps are cost effective.  In the case of the 3/8-16 size eBay has new in the package Irwin carbon steel ones with an asking prices from  $7.95 to $9.95 each.  eBay also has new HSS hand taps by Accupro (7.99 ea.), WIDA ($8.00 ea.), YG-1 ($5.09 ea.).  These are prices for single units.  There are also a number of listings for multiples.  In the case of multiples the unit price for HSS goes as low as $5.00 per unit for name brands.


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## tq60 (Jul 7, 2021)

We have a large assortment of found taps and the usability varies greatly.

Was working a 1 inch steel plate doing 3/8 16 and first set was easy, grabbed wrong drill so a bit over sized but good enough.

Was drilling then tapping with mill.

Next day had correct drill and mill snapped the tap.

Next tap was hard to use so selected a 2 flute hss and it went in like butter.

Hardware store stuff is chasers.

Sent from my SAMSUNG-SM-G930A using Tapatalk


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## ErichKeane (Jul 7, 2021)

FWIW: I use a lot of the Irwin Taps, and they do... alright.  You have to be particularly careful with them, particularly with the smaller ones, and have a REALLY good feel for when they are about to break (OR, invest in a set of Wilton broken tap removers).  I buy them because they are what is available locally... I rarely want to give up on a project for a week because I don't have the right tap size.


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## Richard King 2 (Jul 7, 2021)

It has to be a leaning curve for the OP and all tap users.  We offer our opinion.  I have tried those cheap taps that dull fast and break off, used tap removers that sometimes work, but after using an industrial grade tap made for professionals.  You will get it.  Hobbyist are cheap by nature but quality cutting tools be it an insert or a tap you will get it.     Google the site below and can see the tap he is using is a Plug tap not a bottom tap.  Usually a good tap is shinny and the chap ones are not.   I will never buy a cheap one again as I learned my lessons years ago.  Scroll to minute 3:40


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## ErichKeane (Jul 7, 2021)

Richard King 2 said:


> It has to be a leaning curve for the OP and all tap users.  We offer our opinion.  I have tried those cheap taps that dull fast and break off, used tap removers that sometimes work, but after using an industrial grade tap made for professionals.  You will get it.  Hobbyist are cheap by nature but quality cutting tools be it an insert or a tap you will get it.     Google the site below and can see the tap he is using is a Plug tap not a bottom tap.  Usually a good tap is shinny and the chap ones are not.   I will never buy a cheap one again as I learned my lessons years ago.  Scroll to minute 3:40


Oh, I gotcha completely!  If I had a source of GOOD taps locally, I would have those.  Unfortunately my tap drawer is filled with Irwins because I buy them as I need them :/


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## ericc (Jul 7, 2021)

What brand of tap is in the photo?  It looks a little tired, and there are no markings visible on it.  There appear to be some nicks on the teeth.  There is a huge difference between good taps and bad taps.  There is not as much difference in price.  We had some tapping problems at work.  Seems that the "Made in USA" tap that was bought at Lowes were chewing out threads that caused the screws to strip out.  One of the guys went to Fastenal and bought a "Made in China" tap which was 100X the tap, and it looked better.  There were some complaints about paying $8 for one good tap, but the bad tap goofed up a $100 door part, and ended up taking a long time to do it.  So, we got 1 bad hole from the Lowes tap and 50 good holes from the good tap in less time per hole.  The material was 304 stainless.


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## projectnut (Jul 7, 2021)

ErichKeane said:


> Oh, I gotcha completely!  If I had a source of GOOD taps locally, I would have those.  Unfortunately my tap drawer is filled with Irwins because I buy them as I need them :/


There aren't many places outside the major metropolitan areas that have a good source for cutting or threading tools.  I buy 99.9% of my drills and taps either from McMaster or on eBay.   eBay is less expensive by far, and I use them whenever they have what I'm looking for.  I use McMaster for the times I need them in a hurry or they aren't available on eBay.  McMaster is expensive, but you know you'll always get a quality product, and in my case it's next day delivery.

If you're considering eBay have a list of the sizes and types of taps you need.  Look over the vendors and pick one with a good track record and good prices.  There are a number of vendors that specialize in buying excess stock, and from closing businesses, or those that are changing their focus.  Buy by the package whenever possible.  You may not need 6 or 10 of a particular size today, but you undoubtedly will in the future.  Prices by the pack are in almost all cases considerably cheaper by the unit than buying individuals.

In the past 2 years I've bought nearly 100 taps, and over 260 drills on eBay.  The most expensive taps were spiral flute bottoming taps at a little less than $5.00 ea.  Most were in the $2.00 to $3.00 range, and all were name brands mentioned in an earlier post.  The drills were also all name brands, and far less expensive per unit than the hardware store brands.

I keep my list handy and search eBay for the items I need on a fairly regular basis.  I only buy when the price is right, and only by the pack to reduce cost.  Once you build up a decent inventory you can set an order point and order quantity.  I usually reorder when a particular size gets down to 1 or 2 units.  Then if it takes a week or so to get the order I still can continue to work with what's in stock.


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## MrWhoopee (Jul 7, 2021)

Nobody is cheaper more frugal than I am. I will take a chance on cheap tooling 9 out of 10 times. The 10th time is with taps. The only carbon steel taps (and dies) that I have are in a metric set I bought at a yard sale because it had standard and fine pitches for that unusual situation. I actually used an M6x.75 tap in aluminum to make some special nozzles for my oilers. It worked.

Instead of waiting 'til I have the need, I've ordered several lots of assorted HSS taps and dies off eBay, trying to get all the standards in UNC, UNF and metric. I have gotten some odd ones and duplications, but at about $2 per I don't mind. It's 40 miles to the nearest "decent" hardware store, and I wouldn't buy a tap there unless it was an emergency.


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## riversidedan (Jul 8, 2021)

speaking of taps,  I just made my 1st die part today but had a hard time getting the part to the right size so the die would catch on, yes the part was chamferd>>>>>>>> how can you tell when the part that needs threads is the right size so the die will start????


changing gears>>>>>>>>> yes Ive looked on fleabay at prices and was amazed the diffrence between HSS and carbon !!!  which confirms what you guys keep pounding in my brain. dont worry Ill get it one of these days.......!

changing gears again>>>>>>>that 3/8 16 project has been bugging me so I went to "Tacoma screw and looked at taps. but most were bottom or plug types, I was advised to get a taper tap from someone here  for that project but they didnt have any so didnt get anything, maybe I was wrong but didnt wanna waste the $$ to get back home and find out I got the wrong one. that project still bugs me and needs to be finished. well lets see have a missed anything??? ohya , the part I did today was 6061 and turned out pretty well so the nut went right on, but the threads were a bit shallow at 1st so I spun the die again. for a better job


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## Larry$ (Jul 8, 2021)

Pretty sure you can find all the info you need online for every dimension possible for threads. If you are going to be doing machining I'd recommend you get a copy of the Machinist's Handbook. It can be an older used one since most of the revision stuff has to do with CNC. Buy the full sized version. The tool box version has such small print it is hard to read. Spend a week thumbing through it to get to know what is available. Almost all parts for threading start off a bit under the nominal size.


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## SLK001 (Jul 8, 2021)

You think that a carbon steel tap is cheap?  Spend 6 hours trying to remove a broken CS tap from a part you have 25+ hours into.  If your time has any value to you, you'll find that spending the extra for a HSS tap really makes sense (and saves cents!).


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## Larry$ (Jul 8, 2021)

A plug tap will work. A taper tap is just a lot easier to start. While I'm on the subject, it is quite important to get a tap started straight, I. E, @ 90 degrees. If not the tap will try to drill it's way into the side of the hole and bind up (and break!) If you are using a mill or drill press, don't move anything after you drill. Put the tap into the chuck and manually turn the spindle to get the tap started straight. You can use the end of the chuck key to help turn for a few threads. Then put the tap handle on and proceed as normal. A tap follower is cheap and worth it if you are using the mill where you can keep alignment by just lowering the bed or raising the quill. Get a name brand so it doesn't have a lot of slop. Bigger taps have a centering hole, Taps used with a collet type handle  get to use the recess in the tap handle. Dead easy to get started straight.


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## riversidedan (Jul 9, 2021)

already found that out thru my 1st tapping adventures that I screwed up so I learned to tap using the lathe drill chuck....I kept wondering why the bolt was going into the part crooked  ......uuggghhh


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## Richard King 2 (Jul 9, 2021)

RiversideDan  you wrote " the part I did today was 6061 and turned out pretty well so the nut went right on, but the threads were a bit shallow at 1st so I spun the die again. for a better job"    If your running a die over a shaft, after you use the open end and get a few "shallow" threads, you can flip it over and run the finish side down to make the shallow ones deeper.  If your a rooky I always advise to buy this book.  It is a great one for rookies and pro's.  Be sure to use some cutting oilor tapping fluid for both tap and die.
https://www.amazon.com/Shop-Theory-...ord+trade+school+manual&qid=1625825812&sr=8-1


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## riversidedan (Jul 9, 2021)

...............o


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## aliva (Jul 14, 2021)

Buy a good set of taps. They are commonly sold in a 3 pack, starter, plug, and bottoming.
Cleveland makes a good product. Buy taps as you need them. They can get expensive.




__





						Cleveland
					

Cleveland




					www.cutting-tool-supply.com


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