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Threading arm with screwdriver

Sqerty 4329 12
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Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
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📢 Listen (AI):
  • Good morning.
    I wanted to introduce my next design which is a threading arm.

    The base of the machine is a 400 kg magnetic lifter ordered from a well-known Chinese portal for the sum of 330 PLN.

    Yellow magnetic lifter with a 400 kg capacity lying on a metal surface. .

    I bolted a flat bar to the top of the magnet with a welded 30 mm shaft. I then screwed linear bearings to the 80x80 profile on both sides and put the whole thing on the shaft.

    Person in a green sweatshirt holding the magnetic base of a tapping arm component. .

    The next components of the arm are two 30x30 profiles which are supported by two 120 N actuators.

    Threading arm with a hand holding part of it. .

    The last element of the arm is a screwdriver handle made of 15 mm sheet metal.

    Close-up of a threading arm component with a screw in place. .

    I also decided to make a threading head for the shafts.

    Cylindrical metal component with a hole, placed on a steel table.

    The largest threader I had was 14mm and it went without a problem, but the thread is not very deep despite using a 12mm thread drill.

    Tapping arm with a drill mounted on a metal holder, working on a metal piece. .

    You can see the entire stage from the machine build and testing in the video below.
    I encourage questions and comments.



    .

    Cool? Ranking DIY
    About Author
    Sqerty
    Level 18  
    Offline 
    Sqerty wrote 436 posts with rating 593, helped 5 times. Live in city Ostrowy nad Okszą. Been with us since 2009 year.
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  • #2 21486398
    Anonymous
    Level 1  
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  • #3 21486567
    androot
    VIP Meritorious for electroda.pl  
    I generally like the design, only these linear bearings, as the name suggests are not suitable for the kind of work you are doing. Rotation instead of feed along the shaft. I've used smaller ones and they failed quite easily when forces were applied differently from what the manufacturer intended. They picked up quite a lot of play.
  • #4 21486905
    CMS
    VIP Meritorious for electroda.pl  
    Beautiful construction. And you can see the super "balanced" forces needed to position the "head" in the right place.

    rasputnik6502 wrote:
    I have a feeling that this arm would even be able to handle this screwdriver together with the operator.
    .

    With his wife and children on his lap. :D Robust construction.

    androot wrote:
    Linear bearings, as the name implies, are not suitable for work such as yours. Rotation instead of feed along the shaft.
    .

    And this could turn out to be the cause of any problems in the future.
    Although I think that unless the author is "riding" on it with his wife and children, the bearings under the current load will outlive the author.
  • #5 21487169
    Staszek_Staszek
    Level 34  
    Elegant design.
    In case the unit has to work hard, you can possibly remove the bearings from the housings and insert 30x45 bushings there as pan.
    If you don't have time to do the work, you can buy some ready-made ones e.g:

    Steel bearing sleeve with grooves, size 30x45x40 mm. .

    These linear bearing housings can be cut along the axle and the clearance can be adjusted.
    Alternatively, you could replace these linear bearings with four SK 30 or SK 35 linear shaft supports plus some 30x35 pan.
    I preferred to choose gravity over magnetism when building my Koromyslo.

    Metal structure mounted on a plastic crate. .

    I have two heavy steel blocks with which I can press the Koromyslo against the ground.
    This allows me to drill and thread also in non-magnetic sheet metal of unlimited dimensions.
    My design is a cross between a drill and a drill press and is just plain ugly.
    Here in the layout for fine work.

    Homemade drilling and tapping machine mounted on a blue crate. .

    But I can always rotate the arm and drill into the 'ground'.
    I also didn't use a screwdriver because I like to listen to music.
    I can only hear the rustling of the shavings as I work, but I had to buy respectable motors and spindle holders.

    Congratulations on making a lovely and sturdy drill and tapping machine.
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  • #6 21488150
    CMS
    VIP Meritorious for electroda.pl  
    I don't know what you're getting at with this corom...
    To quote my own statement from about a year ago.

    I know two meanings of the word and neither has anything to do with drills.

    1. koromyslo - a carrier, a wooden device to facilitate the carrying of loads on shoulders, a name borrowed from Ukrainian[1].

    Mainly used in rural households, where it is used to carry buckets of water from a river or well. It is shaped like an overlapping, club-shaped beam with a cut-out for the neck. Two containers of approximately the same weight are suspended from hooks at either end of the bar, so that the load of the coromyser remains balanced.

    Threading arm with screwdriver .

    Source. .

    2) Binding someone in a koromyslo - a kind of Soviet torture, it consists in immobilising the person in such a way that one hand is put behind the head (as if we wanted to scratch the neck) and the other is put between the legs, then the torturers bend the condemned person in such a way that it is possible to fasten the hands with stiff shackles behind the back. Then the torturers bend the prisoner in such a way that his hands are shackled behind his back and he is left in the cell to await the next interrogation.

    Source - Szczepan Twardoch "Chołod". .

    So, please enlighten me as to which part of this machine is koromyslo? I came across this term relatively recently, just in the aforementioned book.
    Because maybe I'm just undereducated, but I've searched on Google and all I see everywhere is a bucket-carrying tool.
  • #7 21488478
    Staszek_Staszek
    Level 34  
    CMS wrote:
    I don't know what you've got with this corom...
    .
    I see a similarity here - the counterweight I used to fully control the pressure of the drill.
    You can't see it in the photo, but there is a double-sided lever (double-armed), the weight of the linear bearing, crossbeam and spindle is transferred to the main column.
    This works similarly to a coromyser, but mine is unequal-armed.

    A woman in a headscarf and apron carries two metal buckets outside. .
    Counterweight mechanism with a drill and technical annotations. .

    If I hadn't balanced the masses of these components I wouldn't have been able to use thin drills.
    I would also have a problem with threading.
    Balanced is also less perverse.
  • #8 21488823
    cirrostrato
    Level 38  
    Years ago I got a "column tapping machine" from a friend, unfortunately it later went to scrap, but in general I remember the construction, the head (something like an ordinary chuck for a column drill) contained one bearing in a strange (I omit the details) simple fixture (two slip rings), hand crank drive, turning clockwise the tapping machine came quickly to the hole, which was to be tapped, then the stroke adjusted itself (there was no automation) to any stroke, then I used various tapping machines, I used a variety of threading machines, the reverse of which caused the tapping machine to go backwards, which it was supposed to thread, then the stroke would adjust itself (there was no automation there) to an arbitrary stroke, I used various threaders, threading, turning in reverse caused the threader to retract, a design to be made by a village blacksmith, at my place, on a really large scale, it worked for five years. I had always planned to make a motor drive but the daily demand for tapping 200-300 holes somehow didn't get me to do it and my older son always earned his ice cream.
  • #9 21489002
    saskia
    Level 39  
    I think such devices are still produced as threading heads, as well as for fine drilling.
    Maybe I can find cross-section drawings of the construction.
    There's a satellite gearbox and something like a clutch, similar in operation to the old bicycle rear hubs.
    A higher load reduces rpm while increasing torque. Raising the head up changes the direction of rotation.
  • #10 21489205
    Staszek_Staszek
    Level 34  
    For threading blind holes and deep holes I make my apologies with a screwdriver
    She 'buzzes' a bit but has an adjustable clutch so I attach her to the Koromysl crossbeam.
    I don't have to listen to music incessantly.
    I don't look for a spindle with a clutch because I don't do production and for a hobbyist it doesn't really matter.
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  • #11 21491942
    gulson
    System Administrator  
    Congratulations, you are in second place in DIY constructions: https://www.elektroda.pl/rtvforum/ranking.php
    And probably immediately in first place.
    Respect.
    If you allow me, I will send you a small gift. Please specify the parcel number.
    Thanks for the presentations!
  • #12 21496588
    Frog_Qmak
    Level 25  
    Forgive the layman's question - what is the measure given at the end of the film?
  • #13 21502593
    Sqerty
    Level 18  
    Frog_Qmak wrote:
    Forgive me a layman's question - what is the measure given at the end of the video?
    .
    The white one? That's the coolant.
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Topic summary

✨ The discussion centers on a DIY threading arm design built on a 400 kg magnetic lifter base sourced from a Chinese portal for 330 PLN. The arm features a welded 30 mm shaft attached to a flat bar on the magnet, with linear bearings mounted on an 80x80 profile to allow movement along the shaft. Two 30x30 profiles are actuated by 120 N actuators, and the threading head includes a screwdriver handle fabricated from 15 mm sheet metal. Concerns were raised about the suitability of linear bearings for rotational forces, suggesting potential replacement with bushings or linear shaft supports (e.g., SK 30 or SK 35) for improved durability. Alternative designs using gravity-based counterweights were discussed, referencing a "Koromyslo" mechanism for balancing forces during drilling and threading. Historical and mechanical insights into threading machines with clutch and satellite gearbox mechanisms were shared, highlighting torque adjustment and reverse threading capabilities. The threading arm uses a screwdriver with an adjustable clutch for threading blind and deep holes, attached to the Koromyslo crossbeam. The coolant visible in the video was clarified. The project received recognition in a DIY ranking, and the creator was offered a gift in appreciation.
Generated by the language model.

FAQ

TL;DR: This DIY tapping arm uses a 400 kg magnetic lifter and two 120 N supports to carry a screwdriver-based head; one expert warning says linear bearings are "not suitable" when the arm also rotates on the shaft. It helps hobbyists build a low-cost tapping arm and avoid the main weak points: bearing play, poor support choice, and base limitations on non-magnetic work. [#21486567]

Why it matters: The thread shows how to build a practical tapping arm from cheap parts, then immediately stress-tests the design with real criticism about durability, balance, and where a magnetic base stops being useful.

Option Holding method Best use Main advantage Main limit
Magnetic lifter base 400 kg magnet on steel Fast setup on ferromagnetic parts Compact and low cost at 330 PLN Not practical on non-magnetic large sheet
Gravity + counterweight base Heavy steel blocks and lever balance Drilling and tapping large non-magnetic sheet Works on unlimited sheet size Bulkier and less portable

Key insight: The arm concept works, but the decisive engineering choice is not the screwdriver. It is whether the guide and support system can handle both feed and rotational side loads without developing play.

Quick Facts

  • The base was a 400 kg magnetic lifter bought for 330 PLN, which set the project’s low-cost foundation. [#21486240]
  • The sliding assembly used an 80x80 profile, a welded 30 mm shaft, and linear bearings mounted on both sides. [#21486240]
  • The arm itself used two 30x30 profiles supported by two 120 N actuators, showing that force balancing was built in from the start. [#21486240]
  • The screwdriver holder was made from 15 mm sheet metal, and the first reported test reached M14 tapping. [#21486240]
  • A gravity-based alternative used two heavy steel blocks and a counterweight lever, allowing drilling and tapping in non-magnetic sheet metal of unlimited dimensions. [#21487169]

How was the threading arm built using a 400 kg magnetic lifter, 80x80 profile, linear bearings, and a screwdriver handle?

It was built around a 400 kg magnetic lifter used as the base. A flat bar with a welded 30 mm shaft was bolted on top, then an 80x80 profile with linear bearings on both sides was fitted to slide on that shaft. The arm used two 30x30 profiles, supported by two 120 N actuators, and ended in a screwdriver holder cut from 15 mm sheet metal. The builder also made a tapping head for shafts and tested it up to M14. [#21486240]

What is a koromyslo in the context of a drill or tapping machine, and how does it relate to a counterweight lever?

A koromyslo here means a balancing lever, not a drilling spindle part. "Koromyslo" is a counterweight lever that transfers and balances load between machine elements, a key characteristic being that it reduces effective head weight during positioning and feed. In the thread, it described a double-sided, unequal-arm lever that shifted the weight of the linear bearing, crossbeam, and spindle onto the main column. That let the operator control drilling pressure more precisely. [#21488478]

What is the white liquid shown at the end of the build video, and how is coolant used during tapping?

The white liquid was coolant. It is used during tapping to lubricate the cutting action and help the tap run through the hole more smoothly. In this thread, the builder identified the white liquid directly and did not describe a flood system or pump. The context shows it as a simple, practical aid used during the build’s tapping demonstration. [#21502593]

Why are linear bearings considered a weak point in a tapping arm that also rotates on the shaft instead of only moving linearly?

They are a weak point because the arm imposes rotation and side loading, not only straight feed. One commenter said smaller linear bearings failed easily when forces acted differently from the maker’s intended direction, and they developed noticeable play. That matters here because the arm slides on a shaft but also twists during positioning. A bearing designed mainly for linear travel can loosen faster under that mixed load pattern. [#21486567]

Which replacement works better than standard linear bearings in this kind of arm: 30x45 bushings in the housings or SK30/SK35 shaft supports with plain bushings?

Both replacements were suggested as better long-term options than standard linear bearings. One approach keeps the existing housings, removes the bearings, and fits 30x45 bushings, which also allows later clearance adjustment. The second approach replaces the bearing units with four SK30 or SK35 shaft supports plus 30x35 plain bushings. The thread does not rank one as universally superior, but both options target the same problem: play under non-ideal loading. [#21487169]

How do you balance the forces in a tapping arm so the head can be positioned easily and thin drills can still be used safely?

You balance the masses with a counterweight lever so the column carries most of the head load. In the example shown, a double-sided lever transferred the weight of the linear bearing, crossbeam, and spindle onto the main column. The author said this balancing was necessary; without it, thin drills would be hard to use and tapping would also suffer. The practical result is easier head positioning with less uncontrolled downward force. [#21488478]

What could cause an M14 tap to produce a thread that is not very deep even when a 12 mm tapping drill was used?

The thread itself reports that the M14 tap went in without trouble, yet the cut was still shallow. The likely cause identified in the discussion is not the 12 mm drill size, but the machine setup: the arm uses linear bearings in a job that also twists the guide shaft, which can introduce play and reduce stable axial feed. Any lost rigidity at the head can limit how positively the tap follows and deepens the thread. [#21486567]

How do gas struts or 120 N actuators help support the arm, and how do you choose the right force for them?

They support the arm by offsetting part of its weight, so the head feels lighter and easier to position. In this build, two 120 N actuators were installed on the two 30x30 arm members, showing that balance was designed into the mechanism rather than added later. The thread does not give a sizing formula, so the practical rule shown here is simple: choose enough support force to balance the head and arm without making the motion fight the operator. [#21486240]

What are the pros and cons of using a magnetic lifter base versus a gravity-and-counterweight base for drilling and tapping machines?

A magnetic base is compact, quick to place, and cheap, but it only helps on magnetic work. The build used a 400 kg magnetic lifter costing 330 PLN, which makes it attractive for steel jobs. The gravity-and-counterweight alternative uses heavy steel blocks and a balancing lever, so it can drill and tap non-magnetic sheet metal of unlimited dimensions. That broader capability costs portability and simplicity. [#21487169]

How can you adapt a cordless screwdriver into a tapping head for shafts or blind holes without damaging the tap?

Use the screwdriver as a low-force drive with a holder and adjustable clutch. 1. Mount the screwdriver in a rigid bracket, such as the 15 mm sheet-metal holder shown. 2. Fix that holder to the arm or crossbeam so the tool stays aligned. 3. Set the clutch low enough for the tap and use it especially for blind or deep holes. One user explicitly preferred a screwdriver here because the clutch limited overload during hobby work. [#21489205]

What is a threading head, and how does a reversing tapping head with clutch or planetary gearbox work?

A threading head is a tapping attachment that helps feed, torque, and reversal during thread cutting. In the thread, it was described as using a planetary gearbox and a clutch-like mechanism, similar in behavior to an old bicycle rear hub. Under higher load, rpm drops while torque rises, and lifting the head changes the rotation direction. That gives controlled tapping without requiring a full production spindle system. [#21489002]

Why does reversing the spindle make some tapping heads retract automatically, and what mechanism controls the feed?

Reversing retracts the tap because the head couples rotation direction to feed direction. One user described an older column tapping machine where clockwise motion brought the tap quickly to the hole, then the stroke adjusted itself to any required depth without automation. When rotation was reversed, the tap backed out automatically. In that account, the feed was self-adjusting through the head’s internal mechanism rather than a separate powered feed control. [#21488823]

What safety issues should be considered when building a heavy DIY tapping arm with a magnetic base and long lever arm?

The main safety issues are overload, unintended movement, and wear that turns into play. This design starts with a 400 kg magnetic base and a long arm, so any shift at the base or guide multiplies at the head. Commenters specifically warned that linear bearings can fail and loosen when loaded outside their intended direction. A second limit is material choice: a magnetic base does not solve clamping on non-magnetic sheet. [#21486567]

Where do linear bearing housings develop play in this kind of DIY machine, and how can clearance be adjusted or reduced over time?

Play develops in the linear bearing units when they are forced to handle twisting and side loads. In the thread, one fix was to remove the bearings from the housings and fit 30x45 bushings instead. The same commenter added that these housings can be cut along the axle line, which allows the clearance to be adjusted as wear appears. That makes the housing reusable instead of disposable. [#21487169]

What should I use for tapping non-magnetic sheet metal of large size if a magnetic lifter base is not practical?

Use a gravity-based stand with counterweight balancing instead of a magnetic base. The example shown used two heavy steel blocks to press the structure against the ground and a balancing lever to control head pressure. That arrangement allowed drilling and tapping in non-magnetic sheet metal of unlimited dimensions. It is a better fit when the workpiece cannot hold a magnet or is too large for magnetic positioning to be practical. [#21487169]
Generated by the language model.
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