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polaraligned
02-11-2018, 08:10 AM
I have this part to make. I have never tapped this long before in any material. I have Mic-6 cast aluminum on hand and will be using that.
My current collection of taps is just common hand taps as I don't have to ability to power tap. I need a reasonably close thread fit.

Thoughts on best tap (gun tap?), possible problems, etc?

https://i.imgur.com/rIyJMSw.gif

MattiJ
02-11-2018, 08:47 AM
I have this part to make. I have never tapped this long before in any material. I have Mic-6 cast aluminum on hand and will be using that.
My current collection of taps is just common hand taps as I don't have to ability to power tap. I need a reasonably close thread fit.

Thoughts on best tap (gun tap?), possible problems, etc?

https://i.imgur.com/rIyJMSw.gif

Your biggest problem might be finding suitable tap. Silver brazing or TIG welding extension shaft could be your ticket..

"nut taps" are typically enough long and thin shank but AFAIK do not come with gun point.

One possible problem with loooong thread like that is pitch errors. Your material is reasonably nice aluminium alloy so I THINK you can get away with it.

MattiJ
02-11-2018, 08:52 AM
Completely another issue is that does it NEED to have this long thread?

Kind of bad design but sometimes you gotta do what the customer wants... :p

CCWKen
02-11-2018, 09:02 AM
I'd go with the weld-on extension or make a tap myself. Other than the height, I like drawings that use all even numbers. :cool:

Toolguy
02-11-2018, 09:13 AM
The best tap for that is a 6" long with reduced shank and spiral point.
https://www.mcmaster.com/#taps/=1biuv9j
Click on screw thread taps, then long reach machine taps.

Mcgyver
02-11-2018, 09:17 AM
I'm betting its your part not a customers? Can we talk about some changes to remove the issue?

Otherwise, long taps and taps with brazed extensions are standard stuff for reaching into dies etc. Braze an extension on a gun point tap, squirt a little wd40 on it, and have at it, probably in the mill.

JCHannum
02-11-2018, 09:20 AM
Taps are available, but not cheap. This is MSC's offering, Victor lists up the 3/8"-16. You might want to contact them.

https://www.mscdirect.com/product/details/64183288

Look for pulley taps, nut taps or reduced shank taps.

polaraligned
02-11-2018, 09:28 AM
I did not design this part. I am going to machine it as a favor for another fellow amateur astronomer.
The original part is a narrow cylinder, about 1", that has a thru hole tapped in it. The problem is that original narrow block rocks too much on the threaded rod and creates a lot of backlash when fine adjusting the azimuth. There is a pin on the bottom of the Tee that rides in a slot, so the threaded rod/block interface is all that keeps it from rocking and creating excessive backlash.

Design comes from here: http://www.gregpyros.com/html/superwedge_azimuth_adjuster.html

Any other ideas are welcome.

Here is a picture of it on the mount:

https://i.imgur.com/hULjhtA.jpg

MattiJ
02-11-2018, 09:52 AM
Bit more complex to make but avoids the ugly long thread:

Make threaded insert(s) and bore the hole to bigger size. Lock the inserts in place with set screws or retaining compound.
Inserts can be also made of better bearing material than aluminum.

Variation B of the above: make the other end insert axially floating(thight slip fit), ie mill a "keyway" to it where end of the setscrew/guide pin can ride.

Lew Hartswick
02-11-2018, 09:54 AM
Well youre BIGGEST problem is going to hit those 4 decimal places tolerances. :-(
...lew...

achtanelion
02-11-2018, 10:14 AM
I would say, if you want a tight long well fit thread, modify the part to use an evanut. Heck, why not go all the way, and change over to a leadscrew? https://www.ebay.com/itm/304014-3-1-2-10-x-36-inch-3-foot-1-start-Acme-threaded-rod-for-lead-screw-CNC-/142078323768.

Perhaps you could change the top of the part to be a tube with a nut at each end and a spring in the center pushing them apart.

There's lots of room there to modify the top, so go for it!

polaraligned
02-11-2018, 10:19 AM
There's lots of room there to modify the top, so go for it!
Well heck, I might as well put in a precision ballscrew with preloaded angular contact bearings on the end.....Not.

I need reasonable as this is just a favor.

MattiJ
02-11-2018, 10:21 AM
Well heck, I might as well put in a precision ballscrew with preloaded angular contact bearings on the end.....Not.

I need reasonable as this is just a favor.

Threaded inserts save you from sweaty hands and 50 usd on buying the tap. About as easy to make as the original and you get added bonus of adjustable backslash.

polaraligned
02-11-2018, 10:22 AM
Bit more complex to make but avoids the ugly long thread:

Make threaded insert(s) and bore the hole to bigger size. Lock the inserts in place with set screws or retaining compound.
Inserts can be also made of better bearing material than aluminum.

Variation B of the above: make the other end insert axially floating(thight slip fit), ie mill a "keyway" to it where end of the setscrew/guide pin can ride.

I was thinking along the same lines as your first suggestion, but if I can tap 3" long reasonably well, then that would be my first choice.

wdtom44
02-11-2018, 10:35 AM
To make it with the option of adjusting backlash out thread one end of the part as you planned and make a threaded bushing with the matching 1/2" thread on the inside. Provide a method for locking the bushing in position, maybe a short section with no threads on the outside of the bushing and a set screw. This way you can adjust out the backlash as it wears, possibly provide a little "pre-load" even. It looks from the picture that you have plenty of room to make the part a little thicker if necessary to get material for a maybe 3/4" or even 7/8" thread on the outside of the bushing.

CCWKen
02-11-2018, 10:43 AM
A problem arises when you have two inserts (one at each end). That problem is that the threads would have to be "timed" to one another. The advantage, though, would allow adjustment of end play.

754
02-11-2018, 10:56 AM
Just buy the extended tap, I used a Guhring, pricey though.
Bet there is cheap ones on ebay.
Get him to buy the tap and you are set.
If he balks at buying tap, it ain't worth a further thought about doing this job..

polaraligned
02-11-2018, 10:56 AM
Maybe the quickest and easiest answer is to use E-Z Lok bushings on each end and lock with a set screw? $8 for a pack of 5.
https://www.mcmaster.com/#90259a163/=1biw3zg

DR
02-11-2018, 11:15 AM
Take a 1/2" coupling nut, turn down and thread about half the outside length to 5/8-18 thread.

On the new aluminum part drill and tap one end for 1/2-13 to maybe 3/4" depth. From the other end of the part drill the remainder of through hole for a 5/8-18 thread. Tap that end 5/8-18 for the special threaded coupling nut. Assemble everything and adjust coupling nut for clocking/backlash and lock in position with set screw from side.

Also, you might reset your CAD system to default to only three decimal places. Showing dimensions to four places implies higher accuracy than is needed. That is especially true if you ever send a drawing out for a quote.


ON EDIT: yes definitely the thread lock inserts could be used. Same idea as mine with the ability to clock the two threads.

Bob La Londe
02-11-2018, 11:15 AM
The other thing if you insist on tapping through is the tolerance of the tap and the percentage of thread you choose to leave (drill size). In aluminum I by default go with 75% of thread. An H2 tap will be tighter tolerance than an H3.

However some of the other suggestions bare merit. A quick and easy method of building in backlash adjustment would be:

Drill through.

Back drill about 2/3s to a larger than clearance size. Exact size to be determined in a moment.

Grab a threaded coupler. Any old cheap one. Turn about two thirds of it round to be a snug slip fit in your clearance hole. Leave a nice hex on the end to put a wrench on.

Drill and tap a set screw hole in the assembly. You can use brass tipped if you want to be able to snug up the position of the threaded coupler with out having it leave a depression like a pointed screw or a cupped screw. This will allow you to make fine adjustments over time without having old depressions shift the piece when you lock it down.

You can use a second set screw behind the first to lock it down and keep it from backing out, or you can use a product call Vibratite.

If you want a little give you can put a washer and a compression spring under the head of the coupler.

MattiJ
02-11-2018, 11:15 AM
A problem arises when you have two inserts (one at each end). That problem is that the threads would have to be "timed" to one another. The advantage, though, would allow adjustment of end play.

Make the inserts with smooth outer diameter without threads or anything, thread them to 1/2"-13 rod and tighten/glue in the hole. Edit: Bob La Londe's coupling nut below sounds about as easy as it gets.
Or use coupling nuts as inserts on both ends and set the inserts in place with Loctite 660 and you don't need to make a single thread ;)


Maybe the quickest and easiest answer is to use E-Z Lok bushings on each end and lock with a set screw? $8 for a pack of 5.
https://www.mcmaster.com/#90259a163/=1biw3zg

Looks like winner except the need for a bit of trial and error to set the "timing" right.

dalee100
02-11-2018, 12:17 PM
Hi,

I see no reason that you need 3" of thread for that part. A standard 1 or 1 1/2 diameter deep thread is more than enough here. So drill each end large enough to make clearance for the threaded rod or tap shank, (which ever is larger), while leaving enough "meat" in the middle to tap. Then use a standard tap.

754
02-11-2018, 12:54 PM
I looked at pics of a few machine taps, they look like the will tap 6x or 5x x dia.
So not a issue.

danlb
02-11-2018, 01:02 PM
I did not design this part. I am going to machine it as a favor for another fellow amateur astronomer.
The original part is a narrow cylinder, about 1", that has a thru hole tapped in it. The problem is that original narrow block rocks too much on the threaded rod and creates a lot of backlash when fine adjusting the azimuth.


Since the problem is rocking of the threaded part, how about simply drilling a cross hole at each end and thread it for a nylon set screw? That would keep the part from rocking and would be a very easy fix with no precision dimensions. It could also be easily adjusted for wear.

For extra points, use a normal metal set screw that presses against a nylon block/pill/puck that bears against the leadscrew.

Dan

Bob La Londe
02-11-2018, 02:19 PM
Since the problem is rocking of the threaded part, how about simply drilling a cross hole at each end and thread it for a nylon set screw? That would keep the part from rocking and would be a very easy fix with no precision dimensions. It could also be easily adjusted for wear.

For extra points, use a normal metal set screw that presses against a nylon block/pill/puck that bears against the leadscrew.

Dan

A few pieces of a milk jug snapped out with a punch work great for that sort of thing.

754
02-11-2018, 02:32 PM
Ok guys when I get home I will measure a machine tap..
Apparently the idea of an off the shelf tap doing the job is too simple, a few on here have to over complicate what can be a simple solution.

LKeithR
02-11-2018, 03:06 PM
...Apparently the idea of an off the shelf tap doing the job is too simple, a few on here have to over complicate what can be a simple solution.

My thoughts exactly. Got a job to do? Buy tap. Tap hole and move on. It often amazes me how far some people will go
to avoid buying the "right" tool for the job...

old mart
02-11-2018, 03:52 PM
I would have a larger through hole in the block with a bronze top hat with the threads in it at each end. One glued/ Loctited and the other just free to rotate, with a screw in the block to clamp it when the backlash has been taken up. With the backlash minimised there will be very little rock in the assembly, and it can be re adjusted in the future if necessary.

MattiJ
02-11-2018, 04:01 PM
My thoughts exactly. Got a job to do? Buy tap. Tap hole and move on. It often amazes me how far some people will go
to avoid buying the "right" tool for the job...

Afaik this was more like favour for a friend than paying job.
I see nothing wrong in a quick redesign if it makes better part, is easier to make and avoids "extra-extra special" tooling

danlb
02-11-2018, 04:15 PM
My thoughts exactly. Got a job to do? Buy tap. Tap hole and move on. It often amazes me how far some people will go
to avoid buying the "right" tool for the job...

It sometimes depends on the budget and time restraints. Other times it depends on what tools you have available to make what you need.

If I have 4 taps in the required size, then it may be days quicker and many $$$ cheaper to spend 10 minutes setting up my welder to extend the shaft on the tap. But then again, I have a stockpile of rod and several different welding processes available so it's not a big deal.

Dan

754
02-11-2018, 04:33 PM
At least 2 taps on ebay for 9.00 or less shipped.

larry_g
02-11-2018, 04:51 PM
Something to stick in the back of your mind. If the block is made as designed and is still a bit wobbly for the purpose, consider boring the end of the threaded hole a half inch deep or so and insert an oillite bushing. Bore the bushing to a close fit on the OD of the threaded adjustment rod.

lg
no neat sig line

Rich Carlstedt
02-11-2018, 05:39 PM
Mic'6, piece of cake .
Will cut cleaner than 6061
Drill it and then tap and you don't need a pulley tap if you measure your taps on hand
I just measured several of my 1/2-13 taps , and you may find that a bottoming tap will allow you to cut 3" and still have a tap wrench on the tap.
My taps would do it

Rich

754
02-11-2018, 05:55 PM
If you make the block as in the drawing, then saw cut thru the middle and down towards the pin on the bottom..not right thru.
You could then drill and tap near the middle, put a screw in there, same plane as the 1/213, and pull the now split thread, together slightly to reduce backlash.
That idea is used on the cross slide nut on my lathe.

Bob La Londe
02-11-2018, 06:09 PM
Wow! Why buy a $50 extra along tap that will only ever get used one time when you can do the job faster, easier, AND BETTER another way with tools you likely already have. I tend to buy tools as I need them, but I do this sort of work everyday.

754
02-11-2018, 06:10 PM
Yeah looks like many normal taps will get thru this.

Bob La Londe
02-11-2018, 06:10 PM
If you make the block as in the drawing, then saw cut thru the middle and down towards the pin on the bottom..not right thru.
You could then drill and tap near the middle, put a screw in there, same plane as the 1/213, and pull the now split thread, together slightly to reduce backlash.
That idea is used on the cross slide nut on my lathe.

A pinch nut does work. I have them on the lead screws of my original toy CNC mill. They work for a while, but do need to be adjusted after heavy continuous use.

polaraligned
02-12-2018, 08:05 AM
I want to thank all of you for your responses. I will try to tap all the way thru with a $8 reground Bendix gun tap from E-bay. If that doesn't work out, I will open the hole up and make threaded end caps as suggested.

Lew- I did not create that drawing, it was supplied to me from someone who has obviously not machined before, hence the 4 decimal places.

Arcane
02-12-2018, 02:44 PM
Some time back I needed to thread a part for a friend and it required a long thread, deeper than what my good quality tap would thread. My solution was to thread what I could and then finish with a cheap tap that had a reduced diameter shank.