Drilling and Tapping of Brass/Bronze

Hi, Bruce!

I don't think you will find too much difference with drilling and tapping the two metals, but then again, I have a Bridgeport and lathe sitting in my garage. I would buy or get a sample of the material and give it a try.

Are you using a cutting oil? Some sort of mineral cutting oil is recommended. You can buy that from MSC (www.mscdirect.com).

I don't know what thread size you are cutting, the thread depth, and load. You could have a look in the Machinist Handbook and do the homework. There are many different kinds of threads and thread tolerances, too. However, you want to work with what is easiest and gives you enough headroom to prevent failure.

I don't know what type of fasteners you plan on using in the threaded holes, but dissimilar metals can cause a galvanic reaction, particularly in a salt environment. Hopefully, the fasteners are only installed for short periods of time. You can also use thread treatments like Antiseize (available as a silver paste in auto stores).

Softer materials can cause the pulling of drills that you experience. You can fix that by altering the attack angle of the drill's cutting edge by grinding the cutting edge flat slightly so that it does not grab the material. However, cutting and tapping with oil will make your job much easier and the resulting thread conform better to the intended thread tolerances.

Hi and thank you for the reply.

I am using 1/4-20 stainless steel bolts to hold on hurricane shutters during the storm and later decorative shutters during good weather. I also plan to use the same technique to mount a lamp or two and possibly an awning.

I tried cutting threads with WD-40 and with the "whatever was on my workshop shelf" oil. As an experiment I poured mineral spirits in an old tin can. The mineral spirits seems to provide lubrication and with thru holes I can dunk the brass several times while it is being tapped and clean out the waste. I don't know if this will work with harder materials. Mineral spirits is probably a sin for mechanical people but this electrical guy seems to be getting away with it.

I Googled the "drill bit grabbing" problem and read a little about the different angles on the drill bit. The local hardware store only has "normal" twist drill bits so I solved my drilling problem by getting threaded rod, drilling four holes in my workbench and bolting the drill vise to the workbench.

Thanks,

Bruce

Definitely use Antiseize on the bolts!

MSC is a great resource for tools and supplies and they can Ground ship from Atlanta warehouse for a one-day delivery (usually) to central Florida.

Lastly, for so many holes buy your taps from MSC and get only the USA made ones. The difference in how well and easy they cut compared to what you buy at Ace or Lowe's will blow your mind (probably cheaper, too). Plus, you get a much better thread that will serve your strength requirements better.

Tapmagic makes a universal cutting oil that might serve you well. Check out:

MSC

I use those cheap acid brushes to brush the tap before entry. The brush not only loads up the tap with oil, but sweeps any chips away from the last tapped hole. Just pour the oil into a small can and brush on the tap.

WD40 works pretty well, but gets a little expensive. The tapping fluid may do a better job than WD40.

How many holes are you tapping?

If you have a large number of holes to tap, you might consider buying a used tapping head for your drill press from Ebay. Not cheap, but it will save your wrist and hours and hours of your time!

I have seen tapping heads but they are a mystery to me. Down pressure makes them turn in one direction and up pressure makes them turn in the other direction? (I assume there is a spring inside and they either engage upward for one direction or downward for the other direction).

Two things really confuse me:

1) It seems like the slowest speeds of the average drill press would thread all the way down so fast you couldn't stop it in time.

2) What about the rule that you tap about half to one turn and then back up to break the waste before proceeding?

I like toys that make my job easier. I just don't understand this one.

Bruce

Tapping heads include a reduction gear set inside. You are right, they have a transmission that when you push the tap the direction of travel is clockwise. When you pull the tap (lift the drill press handle) the transmission reverses and turns out.

You can dive into the threads and out of the threads as many times as you need. An adjustable clutch sets the tension so that it doesn't break the tap. If the tap stops turning, just pull up on the dill press handle and out it comes.

You are probably better off if you did this on a lathe. I just chuck up some bar stock, set a drill in the tailstock, and bore a hole. You can add a knurling tool to the cross slide to put a rough pattern on the outside of the bar, thread the drilled hole, cut the part to length and repeat for the next piece.

Yeah, I like new tools, too, but I would be looking long and hard at something COTS (Commercial Off-The-Shelf) instead of reinventing the wheel and slaving for hours. You are not the only one that has this issue and I doubt that you are the first one to have solved it. If what I suggested for a solution in my other post is not acceptable (I use those same things for inserting into metal, so they are not limited to wood and plastic, just your imagination), search around some more. There are dozens and dozens of suppliers out there besides MSC.

You might also look at 'low-helix' twist, or straight flute drills;

Aforementioned MSC carries both.

Sulfur bearing oils will stain brasses & bronzes. (a patina of brown/black)

_{1) Am I correct that the harder material and more corrosion resistant material will provide a stronger tapped hole and longer service life?}

Not neccessarily. The harder the material the more brittle the thread geometry. Ultimate strength of a thread is determined by amount (%) thread engagement between mating geometry AND both material's composition.

So; a hard bolt into a soft shutter could pull out if the thread engagement is low. A soft bolt into a hard shutter could shear threads off. A soft soft config could create a galling and deformation of both threads. Etc., etc. Though I suspect a little research and typical fits will serve you well.

Just out of curiosity; why are the shutters being threaded? Would not a through hole be more appropriate?

cr3

I am using 1/4-20 stainless hardware. I know that different materials have different hardness issues and corrosion issues. Since a lot of people around here use stainless hardware and lead or brass anchors I assume that they will be "less than perfect" but work.

My shutters are not tapped. They do have a through hole. My main problem is that the house is concrete block and due to both it being old and other issues I have some areas where the block is filled and some areas where it is not. The hardware store does have some lead anchors and lead anchors with threaded brass inserts. For them to work you must strike them pretty hard with a special staking tool. If the block is not filled then hitting them with a hammer pushes them into the block and they fall. I have also had a couple of the anchors in a poured area fail. A friend of mine has had quite a few of them fail. Thus, I looked for another method.

Drilling and tapping my own brass rod seems to be a good solution. Using the shop-vac with the hose turned around to blow the hole out gets it good and clean. A little probing with a screwdriver removes any fractured material. I then rough up the outer surface of the brass with a belt sander and use the expensive 2-part epoxy that is approved for installing rebar in a hole drilled in concrete. So far it seems like a really tough installation that I should be able to trust for many years. Since it is for hurricane protection the cost of a failure could be pretty high.

Thanks,

Bruce

Bruce,

These may save you a huge amount of time! Brass Inserts

They are made of brass and designed for insertion into molded plastic, but since you are epoxying them into the wall they should be just fine. They cost about $16.57 for a bag of 50 (about 33 cents each).

The knife thread inserts (originally from Rexnard in the 70's ??) are wonderful for wood as long as it is not window trim that is held on by finishing nails (hurricane would just pull the trim off the house). But, I need to have clean threads and enough depth that my bolt length is not critical. When I use the concrete epoxy on the wall it looks a little bit like when you set a one year old down in front of a birthday cake and turn your back on him/her. Big mess. I don't see any way that I can keep clean threads and avoid blocking the clearance behind this narrow (approx 1/4") threaded area.

I do like your idea of making it easy but so far I have not come up with a source of materials that I can make work. What would be best would be about 1.5" (or more) of stainless with a hole in it tapped to 1" (or more). I would protect the threads at the front with a bolt and neoprene washer. The rear would either be solid (blind hole) or protected with tape. I would just glue them in and I am done. Good corrosion protection from salt. Stainless bolts would remove all issues related to different materials. So far I can't find any. Thus, instead of going for the gold I am going for the bronze.

Bruce

A search came up with these: http://www.mcfeelys.com/product/3606-SRT/14-20-Stainless-Steel-Threaded-Inserts

I would use 5/16 or 3/8ths here's some choices from macmaster carr: http://www.mcmaster.com/ Type pg 3204 in the find products box there are 10 or more pages of choices.

Stainless on stainless can be a problem, I would 2nd the recomendation for never sieze with copper.

Getting the inserts glued in with out ruining the threads will probably require having the bolts installed.

"Getting the inserts glued in with out ruining the threads will probably require having the bolts installed."

Just plug them with wax.

I keep reading the word "Brass" in this Blog. This covers a wide variety of sins.....

Real (normal) Brass is a mixture of Zinc and Copper if I remember correctly.

This is not good over a long period with regard to corrosion, the zinc gets leached out and leaves a copper honeycomb that collapses easily.

There are versions of brass made more corrosion proof with Tin (or other mixtures and metals), and there are other metals such as Navy Bronze that are better corrosion wise, but I am no expert.....

I just wanted to give you a "heads up" to make sure that what you are using is truly corrosion proof.

By the way, there are special greases (put on and in the threads) to stop high tensile steel bolts seizing in Aluminium engine blocks. These greases are good for any dissimilar metal problem and I feel you should use them as well. They should be available from any good Auto parts store......there they will be far cheaper than anywhere else. Normal grease will help a little, but not as well......

Have a great day.

Too true! Brass goes a lovely pale greenish blue color in a salt atmosphere. Eventually it all goes away. Phosphor bronze merely darkens to a rich brown, and this patina protects it from further corrosion. I also second the protective grease.

If you plan on switching to other metals for your application, I would recommend checking out a table of the galvanic series. It provides goodd data; some of which is what metals NOT to use in a corrosive atmosphere; like don't use brass and alumimum together. Makes a little battery of them that will eventually corrode away.

I guess I just am not getting it here. Why are we tapping Bronze?

Use any number of concrete anchors (per OP's statement of building materials) drill THROUGH the shutter for a clearance of anchor bolt and......voila. The bolts might need be special ordered to bronze, and as stated, threads coated with any nimber of anti-seize / anti-corrosion compounds.

Thank you to everyone that has replied. I'm very interested in all of it even if I am successful in finding an "easy way out".

A few months ago I Googled for several hours and didn't find anything that looked quite right. With a little more Googling this time I finally found something that looks pretty good. At http://www.confast.com/products/hurricane-anchor.aspx they have a corrosion resistant, deep threaded insert that will be pretty flush with the house and allow hurricane shutters to be mounted or removed as required. The concrete threads (overgrown TapCon threads) on the outer surface should eliminate the need for epoxy. The 1/4-20 threads on the inside are "deeply tapped" so I shouldn't have critical bolt length issues. When we do not have storms I can either install sidewalk bolts (keeping the mud wasps out) or try to find decorative shutters. I need to contact them for a better data sheet, but this one looks good.

The knife thread wood inserts are VERY HANDY for wood, but trying to install them in concrete seems like more trouble than making my own inserts. The various wedge anchors and threaded stud anchors just didn't quite seem to do what I wanted, especially where I use metal panels.

In case any of you were wondering, threaded inserts with mud wasp defeating sidewalk bolts in them are only ugly on the side of a house in about 40 states. In southern coastal towns the threaded inserts look so good during hurricane preparation that you don't even notice them the rest of the year.

If anyone knows of other options I would love to hear about them.

Thanks again,

Bruce

I was envisioning glueing in the wood inserts into the concrete.

Thanks, I understood that.

But, my skill at using the special epoxy on the side of a concrete wall makes this option seem like a sticky mess. Keeping clean threads and a bit of a run-out opening in the back also were problems. Installing a temporary bolt during the gluing process seems mandatory. I was doing this with my 1.25" long, 0.5" OD "home made" inserts. I was also using tape to plug the back of the insert to keep wet glue out.

With the wood inserts I guess I could use RTV, wax or something similar to prevent the glue from either filling the threads or permanently gluing the thru-bolt to the insert. It would still be mandatory that the OD of the insert and the actual hole diameter match pretty well. Also the insert must be long enough to hold an approximate horizontal position while the glue dries.

Now that I think about it, a big glob of RTV stuck to the "installed inside end" of the insert (outside the insert) might work out well. It would keep the glue out and provide a little run-thru area for longer bolts. Also, even though I would be ripping it up pretty badly, it would probably act a little like an elastic insert or nylon insert. The bolts might be a little less likely to turn out during long periods of vibration (like a slightly loose shutter during a hurricane).

Thanks to all,

Bruce