So I have never drilled/tapped before but need to do this for an engine mount.

I was wondering just how this is done...I would have thought that drill speed and vertical plunge speed needs to be perfect. For example, if you stop mid-way, wouldn't it "strip" the new threads. I read for plastic it is important to pull the tap in and out several times so as to not cut too much but again, wouldn't this strip the new threads you are making?

I guess I am wondering just how this works (assuming you have a drill and tap set) with or without a drill pres....

I do mine with a hand tap. I usually drill a small pilot hole and then cut a few threads in the mount. Then I back out the tap, claen it and then cut a couple more threads. Just take it slow and never force anything and you'll be fine. There's probably better ways but that's what works for me.

Taps are often sold with the correct size drill required for the pilot hole.

Tapping is most often done by hand, not with the tap in a press or drill. They sell a hand chuck for just that purpose.

If you're tapping metal, the smart money is on the guys who use cutting oil and back the tap out to clear the chips often enough.

For mounting an engine on mounts, I'd wager most mounts are drilled and not tapped. It makes for easier maintenance. It's absolutely strong enough.

Drilling the pilot hole with the drill press is advisable but do not try to put the tap in the drill press or hand drill. Tapping should generally be done by hand.

The key, regardless of material, is to use the correct drill bit for the pilot hole. An easy way to avoid an error here is matched tap & drill sets: http://www3.towerhobbies.com/cgi-bin...&I=LXK370&P=ML

The best thing for driving the tap is to use a tap handle: http://www3.towerhobbies.com/cgi-bin...?&I=LXTHR9&P=7 You can also get by with a small Crescent wrench or something similar if you are careful.

Taps, handles and other stuff are also generally available locally at a hardware or tool store.

I also like this tool for locating the holes in the mount: http://www3.towerhobbies.com/cgi-bin...&I=LXK378&P=ML I know there are more accurate methods but this tool is easy and works well enough.

I think I might have soem step by step pictures on my home PC. I'll take a look later tonight.

Chemie, it's good to see someone do it the right way.

A drill press is really needed. But only because it is dificult to hand drill exactly straight. The hardest part is the layout of the holes on the mounts. It is not a good idea to spot drill the holes through the motor. Few drills ar long enough to allow the drill chuck to clear the head.

So plan out the holes. If you are drilling for a saito, they include all the measurements in the manual Other engines may require you to measure the engine to get the spacing correctly. It also depends on the mounts you are using, Are they independant beams, IE a two piece mount or are they a one piece mount. The basic process is to position the engine on the mounts, so the prop thrust hub will let the prop clear a cowl or side cheeks of the plane. use a small steel scaleand measure from the front of the mount to the front of the engine beam when the engine is where you want it. Now see how much side play you have on the engine, if any. You want the engine to set flat on the lugs and with as little side play as possible, but you don't want to have to force the engine into the mounts. If you have a little side play, split the difference between sides. Now measure from the front of the engine lug the the Center Line of both mounting holes. Most engines will be a standard MM distance, but if you don't have a MM scale, just measure as close as you can, down to at least 1/32" When you have these two meaurements from the engine, now transfer them to the motor mount as lines acrodd the top of the lugs measured back for the line that indicated the front of the engine. Now, measure the Center Line of the mountng holes from the bottom of the engine, IEput your scale across the engine lug so the sqare end is butting against the engine. Measure to the center line of the holes, They will be the same. If you had some side play when the engine is setting in the mounts, add half the total side play to you center line measurements. and scribe front to rear lines across the first two sets of lined. The intersection is where you will drill the holes.

If the mounts are aluminum, you will need to center punch the intersection to allow the drill to start straight and in alignment. It is a good idea to center punch the plastic mounts also. Now, here is where the drill press is really needed. You want the holed to be perpendicular to the mounts both fore and aft and side to side. Iwill usually use a small drill, 3/32 is a good size and spot drill the center punch marks. The small drill will center on the center punch better than a larger drill will, and the small hole will give the larger drill a better center. This spot hole only needs to be as deep as the drill diameter.Now, put the proper tap drill in the drill chuck. Check the screw size,You want the largest screw that will fit the holes. 40 size motors will be either a #6 or # 8 screw 60 size are usually #8 and some largerer motors have #10 screws. In any case use the recomended tap drill for the screw you will use. Center the holes on the drill so when you touch the spot drill hole the drill doesn't deflect . Drill the hole. You will need to use what is called pecking, Drill a little bit and then lift the drill out to clear the chips and then drill a litttle deaper and peck again. Generally three or four pecks are all that is needed. Use less pressure on the plastic mounts as the drill will try to bite a biger cut than it can handle. As to speed, on a small drill likeyou will be using, the fasest speed on the drill press will be best.

OKyou have the holes drilled now onto the tapping. How you procede will depend on the type tap you are using. Generally it will be a "Hand Tap" and you will want to have a Starter tap or at least a plug tap. This references the taper on the end of the tap. The other type tap you might have is called either a Gun tap or Sprial Point tap. These just come on one taper, What I do now is to chuck up the tap in the drill press. Unplug the drill press now because this is going to be done by hand. Center the tap over the first hole. Again moving the vise so the tap doesn't deflect when you lower it into the hole. When I get the hole located OK, Ilift the cover over the pulleys and grasp the spindle pully and turn it by hand all the while applying down pressure on the feed handle. If you are using a standard Hand Tap, you have to break the chips, so turn the tap in about three turns and then back it up a third turn, in another two turns and back it up again. This breaks the chips so the don't ball up and damage the new threads. On something like a motor mount, it is good to back the tap all the way out about two to maybe three times and bursh the chips from the tap flutes. If I'm using a standard hand tap, I'll only got the first depth and remove the chips then move to the next hole because I'll go back later with the tap in a tap wrench and hand finish the holes. You will have established enough threads so the tap will not wander when finishing by using the tap wrench. If you are lucky, and have a Gun or Sprial Point, then you go all the way through the piece in one operation. These taps are designed so the chip pushes down the hole ahead of the tap and will not fowl the threads.

After I have the holes tapped, I like to take a bigger drill and counter sink the threads top and bottom. This is a hand operation, simply hold the drill in one hand and the motor mount in the other an turn the drill about one turn. this will break the corner so you don't have a sharp trhead to try to start the screw into. After this, you should chase the threads by hand one more time incase your conter sink left a little chip in the threads.
If you measured correctly and centered the drill correctly, Things will line up correctly. Measure twice and drill once. Mabey Measure three times and drill once.

Never power the tap into the hole, only turn it by hand either with the drill press spindle pulley (Watch that you don't crank a finger under the belt though),or with that tap wrench.

Don

Wow, those are pretty complete instructions. I've always feared tapping but I think with these instructions I'd try it the next time. Looks like going slow and getting it right is the way to go. I like the idea of using the drill press by hand to get the tap started straight in. Thanks for sharing your process.

This is intended to help with this process, but the drill press trick will also work:

http://www.micromark.com/MICROLUX-TA...TURE,8363.html

Here's a few of the pictures I mentioned. thought I had more complete steps photographed but I guess not. some is better than none though.

1- marking the location for the holes with the GP dead center tool.
2- Holes marked
3- Holes being tapped after drilling
4- Engine mounted

I must have accidentally deleted the picture of the mount in the drill press.

Chuck, good info. The key is to keep things from moving while your are spotting the holes. Using your method, I would add this. Locate , drill and tap the first hole.Mount the engine using just that one hole, clamp down the other side for thrust ailginment, then mark the three remaining holes. drill and tap.

Being the care taker of two cats, Idislike this saying, but it is true, "there is more than one way to skin a cat" There are many ways to accomplish the the mounting of a motor to the motor mount. Many will work and yours is as good as any of them. Otherswill work also, so bring on the other methods. There is seldom a day goes by that doesnt' present me with a different way to dosomething I've been doning for years. Ilook and try each to see if it works for me. Even if it doesn't work for me, it may work for you.

Don

I like that idea. Never thought of it. Generally I try to clamp the engine to the mount when marking the holes. I've even spot glued it with CA on an occasion or two just to hold it in place good enough for marking.

I think the key, regardless of the exact method or tools used, is to plan it out, be as precise as possible and take your time.

In a plastic engine mount, socket head sheetmetal screws work better than machine screws. All you need to do is drill pilot holes. It really helps to have a numbered drill index. Harbor Freight sells a nice set for about $10.
In an aluminum mount, it really helps to use high quality taps...not the junk sold by the hobby industry. Go through an industrial supplier for at least tungsten carbide.
Use Rapid Tap fluid or equivalent.
I chuck the taps up hand tight in a slow speed drill motor and make short work of it. The key is having the best taps money can buy. In the long run they are money well spent.

Thanks for the suggestions. Maybe I will skip the tap as this is plastic mount.

Should I drill and put a lock-bolt on the end (the bottom is flat) or sheet metal screws #8 size for ST090?

Like combatpigg, I use a hand drill for tapping - but only if it's going into a composite engine mount or wood.

Something else worth mentioning is... buy 2-flute taps.

They are stronger and work better than 3 or 4-flute taps. They theory was that the more flutes you had, the easier it was to get the hole straight when hand tapping, but in reality, 3 and 4-flute taps are much more likely to break.

MinnFlyer, why do I have this image of you in a Tu-Tu with your tap shoes on and trying to do the soft shoe

Must have been something you ate Gene, I lost the Tu-Tu years ago

Wont be a Tu Tu , I,ll bet a Hawiain shirt and a pandora . . Thats how I can spot him at the auctions, lol.

Paraffin (kerosene) also is a good cutting lubricant for aluminium, particularly when drilling. A bit messy for tapping.

If one has never tapped before, then I'd suggest practicing on a piece of scrap first.
Unless you're planning to do this on an industrial scale, I wouldn't say that these tapping alignment aids offer good value for money. A taper tap (followed by a "second" then a "blind" or "plug" tap if you wish) in a hand chuck will be sufficient for most through holes. The trick is to start the thread accurately, Place the tap in the hole and, concentrating on keeping it aligned with the pilot hole, turn it gently ahead until you feel the teeth bite. then reverse just a fraction to remove the swarf. You'll be able to feel when it's removed the waste. Repeat again, turning no more than 1/8th turn at a time until you've got 2 full rotations of the tap. Then you can probably increase to 1/4 turns, if the pilot hole is well and adequately lubricated. Aluminium is notorious for grabbing, so it's "slowly slowly katchee monkee". Using the drill press as the alignment tool does work, but my experience of trying that was that the force needed to turn the drill press tended to mask the sensation of the tap cutting and binding. Once aluminium has grabbed something the size of 4mm or so, you're in real danger of breaking the tap and leaving an unrecoverable stump in your engine mount.

I have had sheet metal screws break in mounting engines. I recommend you use metal machine bolt and tap the mount. It will neither break nor come loose. I also use a lock washer between the bolt head and the engine flang. Tapping the mount is not hard to do.

Bruce

Now there is an image that Ican live without!!!!!!

Ken

It's always best if you can use a drill press. It will ensure a straight drill, and a perfectly round drill. (provided whatever you're drilling doesn't move while you're drilling)

Use cutting fluid if you're going into metal or aluminum, for the actual drilling, and for the tapping.

A good, general rule of thumb is drill a hole 3/64ths SMALLER than what you intend on tapping. I.e., if you're going to tap a 1/4 thread, drill with a 13/64ths bit.

16/64ths - 3/64ths=13/64ths...you get the picture. Eventually you'll break a bit on your "matched set" and you'll have to size them up the old fashioned way...

For small bores you'll have to look at a chart to see what #6 #8 #10 screws' actual diameter is....

Whatever you do, take you're time. One of the most frustrating parts of tapping is trying to drill out, or remove a broken tap. Especially if it's just the very tip, and it's 1/2 way down the hole....[:@][:@][:@][:@][:@]

The hard part is getting the holes straight and in the right place. Tapping will be easy, once you have done it a time or two.

Jack

That is the bottom line isn't it Jack

As for broken taps. If it is in a plastic mount, go to the grocery store and buy some Alum. make up a small highly saturated solution of it and water and submurse the mount with broken tap. It will desolve the steel. I'm not sure how it will work in aluminum, but this is a jeweler's trick for removing broken drills in gold and silver. The size of the tap is going to be a lot bigger than most drills a jeweler would use, so It's likely that it could take a couple days or more.

When I was a machine repairman, we used to have a set of tap extractors. Basicly a shaft slightly smaller than the tap drill with three or four groves cut it to it and a collar with three or four fingers that were football cross section. The theory was the you could slide the fingers down in the groves of the tap and then twist the tap back out. I say theory because Iwas only successful using them once. Usually the set had the fingers bent due to prrevious unsuccessful attempts. These were usuallon on 1/4" and above taps.

There is always wire EDM if you are in an aluminum mount. A lot of machine shops have these machines and may burn out a tap for you.

Cost wise though, the alum is probably less than a new set of motor mounts, the other options probably arn't

Don

i have found on the plastic mounts to drill the pilot hole and then chuck up a socket heat bolt in a electric drill ,lube the threads of the bolt and let the drill turn the bolts into the mount, instead of cutting threads they are more like rolled threads

Now this seems an even better plan...

[quote]ORIGINAL: chemie



that works well for plastic mounts as long as you reverse the bolt after drilling it in, drilling the nylon heats the plastic and can really stick the bolt into the mount when the plastic cools.
on all my mounts I tap the threads, and after mounting the engine using longer bolts, I nut the ends, it helps reduce vibration and helps keep the bolts from working there selves loose, having mostly cowled planes I don't have to check the bolts all the time.

the photo also shows the remote glow wire attached to the mounting bolt, I also have used the longer bolts to attach lead balast to the engine mount for balancing the model using a second nut to secure the weight as far forward as possable without securing exessive weight to a cowl.