Tap follower for metal lathe

[Moikle (Michael)]

Hi @metaltechs I am thinking of making a tap follower for my next project on the metal lathe, after @stefanoromano made a comment that we don’t have one but I could make one.

Seems like it ups the complexity from what I have made so far in a few different ways, but I have been thinking it through and throwing together some designs in fusion. I have some questions before I jump headfirst into it though, primarily because I want to better understand the mechanics in play while tapping.

First things first, it seems like it might be a better idea to make it out of mild steel, but so far I have only worked with aluminium and brass. What do I need to learn/be aware of before I can work with steel? perhaps I could make a prototype from aluminium?

secondly, it should be reliably concentric with the tailstock, which as I understand it, requires a morse taper. I think I know how to cut a morse taper if I am able to offset the tailstock and turn a taper between centres, or using an angled compound if I want to make a smaller taper. I also don’t know the specific dimensions of the taper on our lathe (I think it’s a MT 3 based on the specs in the manual, but we also have morse taper sleeves I can use, and I don’t know the best dimensions to use there.)

Thirdly, more a sanity check over my general design:

I think if I am adding a taper, I would add a lip/flange to the green tinted plug section on the right, so the spring would be pushing directly off of the tailstock rather than putting pressure on the screw that keeps the outer barrel on it (the barrel and screw would only be under a little tension while the spring is at maximum extension and not while the whole thing is under load while tapping). I have an extended sheath around the spring as part of the pin, intended to keep the spring straight, and stop it catching, but also to provide a smooth, linear travel as it is supported by a slip fit on the outer barrel.

I considered using a thread to keep the back plug on and provide pre-load to the spring, however this could potentially result in it becoming unscrewed while the tap rotates on the other end (rotational forces could be transferred through the spring) so I settled on drilling and tapping a hole for a screw to hold it in place.

On a couple of these parts - mainly the barrel face and the pin point, it seems like it would require me to remove it from the chuck and rotate it 180 degrees, but this would break concentricity. I can fix that with a few techniques, but I would be interested in knowing the best methods.

[Moikle (Michael)]

Oh, another question, how much force is it safe to put on the tap along the Z axis? both to avoid damaging the tap, but also in case something slips while the spring is under full compression and it were to fire the tap out like a crossbow? just so I can choose the right springs

[stefanoromano]

Hi Michael,

First of all MY APOLOGIES, for the last couple of times I kept calling you Alex… God knows why!!!

On the tap follower, I will try to answer to the best of my abilities, but please keep in mind that I am a hobbyist, and not even a great one at that, so take all I say with a pinch of salt.

@Moikle

First things first, it seems like it might be a better idea to make it out of mild steel, but so far I have only worked with aluminium and brass. What do I need to learn/be aware of before I can work with steel? perhaps I could make a prototype from aluminium?

yes, aluminum would not work on the final product, it needs to be steel (mild is more than enough).

There is an entire range of safety aspect.
you probably need to use coolant
the pressure on the cutter is way higher and it could chip and shoot off, so whear safety glasses.
the pressure on chuck is higher, make damn sure nothing will come loose.
So much that I can’t think of now… in general, be a lot more aware and careful.

Making a prototype would be great to work out order of operations but it has 2 drawbacks:

1. it takes double time and materials
2. it will not help in getting a good finish, alu and steel react so differently on the cutter that a prototype is useful only on order of operations study (still probably worth it in my opinion, but up to you)

@Moikle

secondly, it should be reliably concentric with the tailstock, which as I understand it, requires a morse taper

What you say is true, but a tapping operation does not require the level of precision and repeatability that a Morse taper guarantees. Straight shank in a Jacobs (standard) drill chuck is WAY more than enough. Also, a straight shank one can be used easily on the pillar drill too. I’d say go for straight shank.

@Moikle

I think I know how to cut a morse taper if I am able to offset the tailstock and turn a taper between centres, or using an angled compound if I want to make a smaller taper. I also don’t know the specific dimensions of the taper on our lathe (I think it’s a MT 3

If you really decide to go for a taper please do not DO NOT change any setting on the tailstock!!!
It took us techs literally hours to adjust as it is now!
You can use the compound slide to make a morse 3 taper (wich will fit in tailstock) but again, I don’t recommend it.

@Moikle

I think if I am adding a taper, I would add a lip/flange to the green tinted plug section on the right, so the spring would be pushing directly off of the tailstock rather than putting pressure on the screw that keeps the outer barrel on it (the barrel and screw would only be under a little tension while the spring is at maximum extension and not while the whole thing is under load while tapping).

I am sorry, but I don’t get what you mean there. I am having issue visualising the lip you mention, happy to discuss this in person if you want,

@Moikle

I have an extended sheath around the spring as part of the pin, intended to keep the spring straight, and stop it catching, but also to provide a smooth, linear travel as it is supported by a slip fit on the outer barrel.

This part is very much needed, as the main job of a tap follower is to push and retract maintaining axial stability. You designed it right, and will need to get this working right. there are a couple of alternative designs that could be easier to make while keeping the proprieties of the tip unchanged but I can not explain that in text to save my life. Again, happy to discuss in person.

@Moikle

On a couple of these parts - mainly the barrel face and the pin point, it seems like it would require me to remove it from the chuck and rotate it 180 degrees, but this would break concentricity. I can fix that with a few techniques, but I would be interested in knowing the best methods.

No method is better than others for that. I would suggest chucking in a collet (we have a range of sizes).
This is quick and easy and keeps a very good (albeit not perfect) concentricity.

@Moikle

Oh, another question, how much force is it safe to put on the tap along the Z axis? Both to avoid damaging the tap, but also in case something slips while the spring is under full compression, and it were to fire the tap out like a crossbow? just so I can choose the right springs

Tapping requires a bit of force but nothing close to any amount that could create issues.
To understand, you should be able to easily push the plunger tip in with your finger.

On top of this please remember POWER TAPPING IS NOT ALLOWED UNDER ANY CIRCUMSTANCES.
It is dangerous primarily for you and secondly for the machine.

I know you are not suggesting it, but I felt the need to specify this, for your and others’ benefit.

I think this is an AMAZING project! And I would be happy to help. So glad to see people challenging themselves.
(Yes it will be a challenge, get extra stock, and don’t ask me how I know that) hahaha

Hopefully see you soon!

[stefanoromano]

Also, if you haven’t already, have a look at this video.

Let's Make a TAP FOLLOWER!

[Moikle (Michael)]

Thanks for this great breakdown!

This gives me some useful reference points for my design specs, so thanks!

you might be thinking of @Alex_Wheatley who was here with me haha.

[stefanoromano]

@Moikle

turn a taper between centres

Also, at the moment we do not have all the accessories needed for turning between centres.
In addition to this, no offence, but I would recommend between centres only to the most experienced users, as it is not uncommon to mess up and have the part fly off from the centres.

[VintageSteel (Dave Holmes)]

Hey Michael. Yep. Stefano has you covered.

My contribution is… keep it simple for your first project in steel.

Importantly, removing the chuck or adjusting anything on the lathe bed are very advanced operations and are currently tech only - until and unless authorised.

Happy to assist with this sort of thing though - given a bit of notice…

The three jaw chuck installed on the lathe holds excellent concentricity. Initial workholding and order of operations can circumnavigate most issues should you need to remove and replace work midway. #JustAsk

[Moikle (Michael)]

So if I’m going for a straight shank, to grip in a Jacobs chuck, what is a good diameter and length to fit in that chuck? From what I can tell, all other dimensions depend on both this, and what springs I can buy

[stefanoromano]

I’m quite sure with the big Jacob you can go up to 15 or 17mm outside diameter, but I would check that first of all.

Goes without saying that the bigger you go, the easier it is to make (although will use more material).

If you are planning to leave the follower for members to use, please feel free to grab a suitable steel bar from the stock.

[Moikle (Michael)]

I see, 15mm for an OD for the whole tap follower seems pretty small. my first design was 19mm. Might need to give it a separate shank at the back.

[Moikle (Michael)]

Here is a redesign and dimensions that I plan to cut to (not accounting for fit tolerances)

Assembly:

Barrel dimensions

Shank dimensions

pin dimensions

I might need to adjust some of these dimensions to fit collets/drills/tooling, but it’s all built parametrically in fusion so I can just type in new numbers to get an updated design.

[stefanoromano]

I don’t fully understand why you got the cross screw joining barrel and shank…
Why not thread one into the other?

[stefanoromano]

Oh rights to avoid rotational load unscrewing it, but I don’t think that is possible to happen…
A tap follower is used only when tapping, which 99.99% of the time is done screwing the tap in, so the rotation will tighten the barrel on the shank rather than loosing it.
Isn’t it? I may be wrong

[Moikle (Michael)]

Yeah it was more necessary in my first design, where the barrel was the part that gets gripped in the tailstock. The plug would have been unscrewed instead by the same rotation. (When the barrel is gripped, and the rotation is sent all the way through to the other side, a clockwise rotation becomes an anti-clockwise rotation)

Now that the shank is connected to the plug, there should be no real rotation force between it and the barrel, meaning i could thread it, and it would work fine, even for left handed thread cutting. All rotation forces are sent through to the tailstock. Threading the barrel on actually probably would be better, providing a more secure support for the sliding action. Now that the barrel isn’t gripped, lateral forces could cause it to wobble against the shank and then the pin would end up wobbling by extension. A screw thread should be more sturdy i think

[stefanoromano]

I had 10 min spare in the office and I made a design that keeps it super simple and I think functional.

I couldn’t be bothered to model the spring, but it is obvious where it goes.

Have a look and let me know what you think.

[stefanoromano]

I reckon the most challenging feature is this chamfer deep in the bore

I am really unsure on how to do it!

But it could still work with a square bottom, or even with the chamfer left over from drilling

[Moikle (Michael)]

That “chamfer” is actually me trying to account for the angled profile of the tip of the drill, so i have a matching (external) chamfer on every part that touches the end of one of the bores. That angle is another thing that i made an editable parameter of the design. I currently have it as a placeholder value of 30 degrees

So it’s actually the easiest part, not the hardest

[dmagliola (Daniel Magliola)]

Just my 2 cents: (first of all, i love how you’re approaching this!)

While I agree you probably want a straight shank for this, I want to comment on your idea of cutting a Morse taper, in case it’s useful for a future project.

Cutting a Morse taper is not exactly rocket surgery… But it’s not a very beginner friendly thing to do, in my opinion. If you need to do it, you are generally better off buying a “soft blank” (Morse Tapers tend to be hardened, so you can’t buy an existing one and machine it easily)

Here’s an example of what i’m talking about: https://www.chronos.ltd.uk/product/soft-blank-end-arbor-3mt-tang-end/

Some keywords you might find useful are “soft morse taper”, “morse taper blank”, “{X}MT Arbor blank” ({X} being the number of taper you want), etc.

These are a basically Morse taper cut out for you already, but unhardened, which a large cylinder at the “head”, that you can machine into whatever you need. Generally a threaded hole or bolt, where you’ll attach other things. Or in this case, you’d bore it to make the space for spring and the follower itself, and probably screw in a “cap” at the top (The opposite end of how you’re doing it here).

After that, you get to choose whether you want to harden it or leave it soft. I believe Soft is probably good enough for most uses, but i’m extremely not an expert on this one.

Anyway, wanted to leave that here in case it’s useful in the future!

[stefanoromano]

@dmagliola

These are a basically Morse taper cut out for you already, but unhardened, which a large cylinder at the “head”, that you can machine into whatever you need

amazing piece of information.

I wasn’t aware of this possibility!

Still think for this straight shank is the way forward, but super useful to know!

[VintageSteel (Dave Holmes)]

We have a spare soft taper I think.