The Unofficial Mamod and Other Steam Forum

mogogear

As I progress with metal working - and trying to knock out some displacement oilers...I have hit a snag

I have found tapping charts that show what size drill bit should be used in conjunction with a matched tap size.....makes perfect sense!

So I have a 3/8 NF 24 tap that requires a letter Q drill ( or 21/64 closest fractional) for the hole to be drilled.( i only had a 21/64)

Question:
So to cut external threads with hand dies- is there a corresponding chart with O.D. specs to be used for the external die that matches my tap?

It seems there should be a counter-part to the tap chart for the die's... and I have found some diamters listed on the tap chart ... like .3320 that seemed like they would be what I needed.

But when I use the 3/8 NF 24 die on a piece of stock turned to that O.D.--I get a very loose fit in the tapped 3/8 hole.

Second Question?

Is this because I didn't have a letter Q drill and the 21/64 drill I used made the die cut male threads too loose?? or is the die end the problem?

So I come to you ...any of you that can help me see what I am missing..

I hope I explained myself well enough to be understood!!
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers

tmuir · Posted: Tue Nov 03, 2009 4:42 am Post subject:

If you have a 3/8 inch thread you want to put onto a rod. The rod should be 3/8 inch with a very small chamfer at the start to help the die start and to stop you having a very weak thread at the start that can be snapped off.

Also if you have a spilt die they are actually adjustable.
SOme of the split dies have a screw you do up which widens the gap and makes the thread slightly oversize.
Others work by having two dimples, one on either side of the split and by doing up the srews in the holder tighter closes the die.

You should first cut the thread oversize and then do a second pass with the die closed up a bit to give the correct thread size.

It is possible to close them up too much and make the thread undersize so it would be a sloppy fit.

Also cheap taps and dies are just that, cheap.
If you have a cheap set you may find they give sloppy results.

As a side note for most model engineering work you only need between 65% and 70% thread engagement.
Once you go above 70% the cahnces of snapping a small tap goes right up.
You can see many different charts giving different sized drills for the same thread and a closer look at the drill sizes and you may find some give you as much as 90% thread engagement which puts the changes of snapping a small tap through the roof.

I have made charts for ISO meteric and ISO metric fine, BA and BSW which if you want I can PM to you tonight when I get home.
_________________
http://www.freewebs.com/ozsteam/index.htm
http://members.iinet.net.au/~tmuir1/

A nice example of an Australian made Scorpion Donkey Engine

tmuir · Posted: Tue Nov 03, 2009 4:55 am Post subject:

Just remembered I have the BA and metric ones on my work PC so will upload them to this thread now.
Will add the BSW tonight.

Click to download file

Click to download file
_________________
http://www.freewebs.com/ozsteam/index.htm
http://members.iinet.net.au/~tmuir1/

A nice example of an Australian made Scorpion Donkey Engine

GUTMACH · Posted: Tue Nov 03, 2009 5:16 am Post subject:

Drilled holes to be tapped, are drilled at the nominal diameter of the threads. With a 24 per inch thread, not alot of holding material there.

A drilled hole is not a round hole, and tends to be over size due to sharpness of the drill, speed and feed.

A drilled hole with a 21/64th drill should produced a hole within the .3281" diameter range. Tolerances for the type of hole you need is between .333" and .338". I think you will be fine if you are close to the .333" diameter

The threaded part is turned to the major diameter of the threads, in this case, for the 3/8-24, the O.D. should be .343", no less than .340"

Most of the above information came from the Machinery's Handbook, 23rd Revised Edition.

By the way, if you had bought a tap and die set, there should be a tap and die chart included.

Hope this helps,

Wayde

scorpion2nz · Posted: Tue Nov 03, 2009 5:26 am Post subject:

I have found

Drills,Taps and Dies by Tubal Cain
workshop practice series number 12

a book well worth the money i spent on it

mogogear · Posted: Tue Nov 03, 2009 5:32 am Post subject:

Ok you helped a lot there. I am glad my assumption for a 3/8 thread should be the decimal equivalent to 3/8 and so on.

I do chamfer the end- that was one of the few things I knew from metal shop.

You hit the nail on the head with this pearl of wisdom...I have some cheap taps and dies and my job most likely would have gone smoothly had I a nice set. They are not the nice adjustable type I use them so infrequently I was hoping they would be ok.. they are Sh@@ for sure.

I am making some displacement oilers for lathe practice and just knocked out another using a 5/16 I.D. bore in a 3/8 brass rod. This allowed me to use a different set of tap and dies mates..It worked much better . In addition to cheap taps and dies I have only a 29 bit drill set..and am missing the incremental sizes.

My next plague will be the fact that there are so many different threads used in the hobby world. Learning curves... they are what they are.

I need a knurling tool as well- it is hard to make caps that you can get a grip on without one..Tooling - just when you think you are doing OK- there is more to buy...But I am having fun--!

Thanks for the good advice Tony.
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers

tmuir · Posted: Tue Nov 03, 2009 6:55 am Post subject:

tmuir · Posted: Tue Nov 03, 2009 7:00 am Post subject:

An easy solution for no knurling tool where grip is more important than looks is just get a course file with on the geooves (can't think of the corretc name) only going one way, so not a diamond pattern.
Place the item that wants knurling on a hard flat surface and press the file down hard on it and roll the file across it.
You will find it will have imparted the file pattern to the brass and will provide a bit of grip. Not as good as knurling but will do.

I now buy each tap and die as I need it and buy high quality HSS ones. They are expensive but work very well.
I also at the same time buy the correct size drill for the tap and keep it with the tap so it is not used for regular drilling.
_________________
http://www.freewebs.com/ozsteam/index.htm
http://members.iinet.net.au/~tmuir1/

A nice example of an Australian made Scorpion Donkey Engine

tmuir · Posted: Tue Nov 03, 2009 9:53 am Post subject:

Here is the BSW chart I made.

Click to download file

ANd since I'm putting up charts here is my little one for cutting speds.
It works for drills and parts on the lathe.

Click to download file
_________________
http://www.freewebs.com/ozsteam/index.htm
http://members.iinet.net.au/~tmuir1/

A nice example of an Australian made Scorpion Donkey Engine

scorpion2nz · Posted: Tue Nov 03, 2009 9:56 am Post subject:

alternative to knurling tool
is a of vicegrip pliers I hold them at an angle to the work and close up hard then release and move it around and close again and so on you will find that when you have gone around in a full circle the other jaw imprint was at right angles to the top one then just a quick sand and all done
if need photos just ask

ozsteamdemon · Posted: Tue Nov 03, 2009 10:34 am Post subject:

All drill bits cut oversize , even new ones , for precision work i double drill or triple drill .
_________________

alan2525 · Posted: Tue Nov 03, 2009 11:58 am Post subject:

A few broken taps along the way is all par for the course. With the smaller sizes of BA taps I try to buy a few of each taper and second. It's really annoying if you break a tap and don't have a spare in stock, likewise a few of each of the smaller tap drill sizes.

After a while there will be certain sizes of threads that you will use regularly and although taps and dies are expensive it's worth paying a little bit of a premium and buying from a reputable model engineering supplier.

A lot of engineering companies will sell HSS taps and dies at a premium price which are still only cheap low quality Chinese imports. The thread formed can often be quite poor quality and I'm never convinced that the steel is really HSS if it's from China. Many of their cutting tools are poorly hardened and tempered too and will quickly lose their edge or snap in an important part. Dormer are always good quality and made in accordance with insustry standards, with much more stringent quality control.
_________________

For Custom CNC Engraved Nameplates and Worksplates
http://www.loco-plates.co.uk

tmuir · Posted: Tue Nov 03, 2009 12:02 pm Post subject:

The ones I buy are made in England Alan.

_________________
http://www.freewebs.com/ozsteam/index.htm
http://members.iinet.net.au/~tmuir1/

A nice example of an Australian made Scorpion Donkey Engine

mogogear · Posted: Tue Nov 03, 2009 4:19 pm Post subject:

Thank you all for sage advice- I am sure others will need it as well. The fact that drills do not drill the size indicated is a small revelation in it self.

I will make stepping my drilling up in increments a new habit all the time in precision work.

I will get a knurling tool- but a QC toolpost from these people http://www.a2zcnc.com/machinetools.asp is first on the list of upgrades for the 618..then the knurling tool. also the round profile from RDG http://cgi.ebay.com/RDGTOOLS-8MM-...PowerTools_SM?hash=item56330be3f4

Cedge and Bogstandard always got such good results - they will be a splurge to see if I like them also!

thanks again
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers

mogogear · Posted: Tue Nov 03, 2009 9:08 pm Post subject:

I am kind of a goofball when it comes to getting the right tool when the need hits...So after realizing the Harbor Freight tap and dies were crap...

I found this MATCO set

# 5/8" and 1" hexagon dies
# Taps and dies for 17 fractional and 17 metric sizes, plus the related tools
# Includes 5/8" Hex Dies - 3mm .50, 4mm - .70, 4mm - .75, 5mm - .80, 5mm - .90, 6mm - 1.00
# 1" Hex Dies - 7mm - 1.00, 8mm -1.00, 8mm - 1.25, 9mm - 1.00, 9mm - 1.25, 10mm -1.25, 10mm - 1.50, 11mm - 1.50, 12mm - 1.50, 12mm - 1.75, 1/8" - 28BSP
# Pipe 1/8 - 27 NPT, 1/8 - 28BPS
# 5/8" Hex Dies: 4-40NC, 6-32NC, 8-32NC, 10-24NC, 10-32NF, 12-24NC
# 1" Hex Dies: 1/4-20NC, 1/4-28NF, 5/16-18NC, 5/16-24 NF, 3/8-16NC, 3/8-24NF, 7/16-14NC, 7/16-20NF, 1/2-13NC, 1/2-20 NF, 1/8-27NPT
# Taps matching all of the above dies stock
# DS4H - Adjustable Die Stock
# TW9 - Adjustable Handle Tap Wrench
# TW3 - T-Tap Wrench with Hex Nut
# TW4 - Tap Wrench with Hex Nut and 3/8" Square Drive
# SG514 - Fractional Screw Pitch Gauge
# 6312-S - Metric Screw Pitch Gauge

http://www.matcotools.com/Catalog...p;cat=2417&select=&page=2
( about 2/3 way down on the page--117pc) used on Craigslist ....about an hours drive away......$100 cash........

Did I do alright?

Now I feel better...I think

Now to put my old taps and dies on Craigslist...$15 each set...I am out $70...
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers