3D Printed Threads Modelled in Fusion 360

I recently posted an idea for a 3D printed depth setting jig for use on my Myford Big Bore lathe. A couple of readers had run the STL files and struggled with the fit of the mounting boss thread (M35 x 1.5) that mates with the thread on the end of the lathe spindle. This is a known problem with 3D printed threads where the accuracy of the 3D printer and the size of the thread being printed can interact and have an impact.

Fusion 360 does not have a tolerance tweak in the thread creation tool. This is not a problem in that you can use the Face Offset tool to adjust the thread geometry. This does not take long to do. The process also allows you to add fillets to the thread peaks so they are less aggressively ‘sharp’ and therefore more likely to survive longer.

Select the Inspect/Section Analysis to view the cross section of the thread to be adjusted. Choose any axis for this. Manipulate the view so you can see the cross section face and the around to the side of the 3D model. Do the tweaks shown below by selecting the appropriate faces of the thread and making an Offset Face adjustment and then adding a chamfer. The difference is very minor but it makes the thread less ‘sharp’ and aggressive to its mating half which is likely to be a metal component. If you are working with a modelled threaded hole rather than a rod then the changes are the same. The values shown are nominal and will change with the modelled thread size. If you overdue the offset the thread will become very sloppy.

The only tricky part is Manipulating the view in Fusion to allow the appropriate face selection otherwise the Offset command is straightforward.

To a degree some of this could be achieved in your 3D slicer but adjustments would become global rather than specific to just the thread geometry.

If you want a more detailed explanation then I suggest you watch Kevin’s post on Product Design Online.

I have modified the geometry of the Depth Setting boss threads to give more tolerance and reposted the STL to match on the link below.

If you have a Myford Small Bore lathe and would like to send me the bore size and end thread I can create a new version of the depth setter to match.

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Three axis stepper controller PCB in stock

Some while ago I described how I had fitted stepper motors to my Myford VMB milling machine. It was not the intention to convert the mill to CNC but simply to give my arms a rest winding handles back and forth. This was particularly so with the Z axis. The secondary advantage is that the motor driven movement leaves a much smoother finish than my hit and miss erratic winding of the hand wheels.

The design is Arduino based and allows selection of a single axis at a time with variable speed control in forward or reverse direction together with the option to fit limit switches/emergency stop facilities. The PCB, with appropriate stepper hardware, could be applied to any other machine needing motorised movement.

You can read the full article here.

Following some recent publicity of the conversion, I received a number of requests for the unpopulated printed circuit board. I now have a few of these left in stock if anyone is feeling adventurous. Here is a view of the external connections needed.

This conversion started off as a ‘I wonder if I can’ and is now probably one of my favourite projects in terms of its impact on my day to day use of the VMB.

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Myford Super 7 Large Bore depth stop

I recently had to turn a number of items on my lathe and wanted them to be consistent in length. These were long items, too long to reference with my home made Morse Taper depth stop.

In desperation I raided my Sherline CNC Rotary Table hardware kit for my coaxial tailstock clamp. This is based on the Myford tailstock winding handle but without the handle. It clamps the lathe bore to the CNC table for cutting items needing indexing such as clock wheels. Wheel cutting is quite a demanding application. There is no tolerance for slippage or you will get to the last tooth and have only half half the material that you expected left to cut … and the box of shame looms.

The clamp is quite simple – the main body is an expanding collet, this mates with an expansion cone and a centre threaded rod. The cone angle is 5 degrees. There is a knob to tighten the assembly and squeeze the cone into the body to expand its arms. The body has four slots that two pins on the cone engage with to stop rotation.

Having finished the particular job in hand I put away the Sherline clamp and thought it would be useful to make a second version of the clamping collet dedicated as a lathe depth stop. I was rummaging in my metal stock for material to make this when the light bulb came on …. why not 3D print it? When the clamp is used as a depth stop there is no rotational stress. It just acts as a stationary reference stop that sits down the lathe bore.

I copied the dimensions from the Sherline version and input this into Fusion. I printed the body, the cone and a knob (with an M8 embedded nut). The centre rod is M8 studding which passes through the collet body and then screws into the cone and then protrudes onwards to set the depth in the lathe bore. You would think that there needs to be a nut to lock the studding to the cone but the cone cannot rotate as it has the two locating pins. Providing the studding is stopped from rotation while the knob is tightened, the depth should be set solidly. A lathe depth stock is rarely an accurate setting tool but just a repeatable reference. The accuracy of the final cut is catered for by the tool position set and the various lathe DROs.

Printing this was a lot easier than cutting it from metal. No messing setting cutting angles etc. Here is the Fusion pictorial view and cross section.

After using it a couple of times I ended up putting a spring and two M8 washers between the body and the knob to maintain a slight pressure on the cone. The spring keeps the locating pins engaged in the slots on the body as the assembly is pushed in place down the spindle bore.

I also added a ‘top hat’ on the end of the M8 rod (not shown above) to give a larger surface area for the work piece to bear against. This would also stop wobble of the threaded rod as the spindle rotates.

Attached below is a ZIP file with the body, cone, top hat and knob STL files. You will need some M8 studding, an M8 nut and some short M3 stubs for the anti rotation pins in the cone. If you add the spring then two M8 washers will be needed. All the threads are modelled in the STL files but will need cleaning up post printing. I printed in PLA+ and had the prints set to four perimeters. I superglued the two M3 studs in place. The tops of the studs should not protrude beyond the unexpanded body surface otherwise they will bind on the inside surface of the spindle bore.

Things now went a little bit off piste …. I had forgotten that the end of the lathe spindle has a threaded section that mounts the bearing pressure collar. The exposed thread is normally protected with a plain collar. The thread is M35 x 1.5, something very easy to model and print via Fusion 360. Below is the relevant exposed thread with the protector collar removed.

Another light bulb came on (getting to be competition to Blackpool you might think). Why not make things very much simpler?

I modelled a boss to screw onto the M35 x 1.5 thread with a central core to fit down the spindle bore (26mm) and with a central M8 tapped hole. I also printed another through hole M8 knob, a M8 top hat and a new blind M8 knob. I now had a much more simple depth stop.

Here is the Fusion image of the boss. This would have been tricky to cut as one piece in metal but very simple as a 3D print.

Here is a close up view of the final assembly with the top hat out of shot at the far end of the M8 studding but shown in the second image. The knob on the left grips the end of the studding to allow easy adjustment of the position of the top hat. The inner knob locks the studding in place against the boss. Both knobs have embedded M8 nuts glued in place. (Note the bend on studding is a photographic distortion).

Two solutions for a depth stop. The second option is peculiar to the Myford and the first solution more universally adaptable to other lathes. The following download ZIP file contains the STL files for both versions and there is a second ZIP which has the Fusion 360 model for those wanting to tweak. Either version will make a useful addition to the workshop tooling.

Update : I had comments from some readers that the internal thread on the boss was very tight mating on the spindle thread. Being 3D printed it will depend on the slicer and the 3D printer for its fit. I have tweaked the Fusion 360 model to be more tolerant of this and new STL file is on the link below. See the later post on how to do this.

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Tangential Lathe Toolholder for Myford Super 7

Yet another design to add to the plethora out there

The concept of a tangential lathe tool holder had passed me by until Blondie Hacks mentioned it in one of her YouTube posts.  This resulted in an hour or more lost down an internet rabbit hole.   The conclusion seemed to be that I was very late to the party.  There are many designs out there which include the Eccentric Engineering commercial item.

I quite liked the look and simplicity of Mike Cox’s design. With the knowledge gained from my unintended meandering internet research, I tweaked it slightly and committed it to Fusion 360. This is shown in the pretty picture below.   Note my design was to be mounted in a QCTP on my Myford Super 7 and is intended to hold a 3/16” HSS tool. Here is my Fusion 360 image of the model.

The following ZIP file contains my full write up along with the Fusion 360 model for the toolholder and an associated 3D printed sharpening jig.

Update : This tool is very good. It can tolerate decent depths of cut and leaves a nice finish both turning and facing.

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Hemmingway Sensitive Knurling Tool

A rite of passage ?

You may have watched James at Clough42 and Brandon at Inheritance Machining both make the Hemmingway Sensitive Knurling Tool (HK# 1115) and shared their experiences. In the past I have made a few Hemmingway kits and always enjoyed making them and the associated learning process. I decided to add the knurling tool to my collection.

Like James and Brandon I found the drawings beautifully presented but a little dyslexic with imperial dimensions showing as a mix of fractional and decimal units accompanied by metric equivalents. To get more intimate with the design and to circumvent the fraction and decimal imperial dimension issue I resorted to redrawing the design in Fusion 360. Fusion lets you set an overall dimension standard for a drawing but you can enter an individual dimension in any format or standard. Fusion will then display the individual dimension at the default drawing standard. This allows you to enter any dimension in mm, fractional Imperial or decimal Imperial. I find this a convenient way to better interpret the Hemmingway drawings. Redrawing in Fusion also highlights the potential problems in the rounding of metric dimensions from the imperial entries.

James and Brandon both resorted to traditional methods for the construction. This involved using a rotary table for the curves (of which there are many on the two jaws). I will now add further to my reputation of being a lazy engineer. Having redrawn the design in Fusion it was a logical step to produce the kit with CNC assistance.

While CNC might make the construction appear easier, it still creates headaches on work holding. This is magnified by the fact that the kit is supplied with ‘final size’ material. Brandon took this further by skimming all the supplied stock but then fell foul of the subsequent impact of this on some parts.

The CNC machining of the side plates, jaws, adjuster plates, spacer block and mounting block all went well to my CAM processes. This required sacrificial mounting plates and lots of checking before hitting ‘GO’. I am pleased and relieved to report no dings resulted from the CAM.

The majority of the remaining parts are lathe activities with, where needed, a liberal use of a collet block for cross drilling . I cheated on the adjuster thread and used M8 threaded rod with appropriate dimension changes to its mating components.

I had one post CNC ding on the lower jaw leading to an additional M3 hole. The lower jaw nut was the most probably the most tricky part. That aside all went to plan.

I used the semi finished tool to knurl the adjuster knob and pressure lever knob and was very pleased with the clean knurls that resulted. Here is my finished knurling kit mounted on a Myford QCTP holder.

Would I recommend the kit ? Yes – but it has some slightly advanced activity needing careful planning and thinking. The drawing dimensioning can catch you out. I think redrawing in Fusion helped highlight and clarify these issues. Measure twice and cut once is the order of the day particularly with respect to shaping the jaws. If you have CNC then this is a much easier way to go once you have got your head round the necessary work holding.

Note – the kit does not contain the knurling wheels so you need to order them separately.

Overall this has been an interesting and challenging project. I now have a very useful asset added to my workshop tooling.

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