Lathe – Threading gear calculator

Having bought a lathe for various DIY projects back in 2015, i quickly discovered the need to cut some unusual thread pitches (Astronomy adapters in particular have some of the weirdest out there).

The lathe manual (or the housing of the transmission system :D) , usually provides some information regarding the gearing for the most used ones, such as 0.05mm, 0.1mm, 0.2mm, 0.4mm, 0.5mm, 1mm and so forth.

But nothing for lets say an M42x0.75 adapter widely used in photography and astronomy!

While looking through the web in 2016 for a lathe gear calculator there was none to be found, that took into consideration the spindle to gear A ratio.
The spindle in this specific lathe (and many other brands from what i have read ) has a ratio of 4.5 turns. So in order for gear A to make a full turn the spindle makes 4.5 turns.

Without this number the usual quadrant calculations for gearing lathes, obviously fails and your thread pitches are not what you have expected at all 😛

Here is a very crude calculator for finding out possible, combinations of gears in a metric lathe (that is, a lathe with a metric leadscrew although it can cut some imperial threads by approximation), in order to produce the desired pitch when cutting threads!

Do note that some of the produced combinations, are not feasible at all for the time being, but I will upgrade it when time permits.

Lathe threading gear calculator

Have fun!


DIY Telescope mount pier HEQ5 PRO

The bane of astrophotographers is, in my opinion, the routine of setting up and dismantling the gear on every session. As time accumulates this becomes a rather tiresome process, hindering the excitement of astrophotography where the need for really accurate polar alignment is paramount.

That is where a permanent installation, a.k.a pier comes into play (provided you are ok, to just securely cover up your gear for protection of the elements).

My mount is a skywatcher HEQ5 PRO Synscan, though the pier can host any type of mount by changing the top adapter.

The design had to comply with the following goals :
a) The leveling of the pier would be on the bottom and it would have to be massive for two reasons:
— Contrary to popular belief, the top does not have to be level. It is better to have a really stiff top since you will be doing drift alignment anyway with a permanent setup.
— There is no point, mechanically speaking, to mount a 40kg steel tube on M13 rods (there alot of tops in the internet with M13 bolts for adjustments which just scream flexure with anything heavier than an ED80 and even more so the same goes for the bottom design
b) There would be no holes in the rooftop in order to protect the water seal in the construction.

So here is the photo story of the building!

Measuremements of the baader adapter for HEQ5 PROTaking the approppritate mesurements for the fitting the HEQ5 PRO head adapter to pier’s top plate.


Preparing the top plate of the pier HEQ5 PROUber lathe work on aluminium by my brother in law (Thanks Tom!)

Finalized top plate of the pier Finished product, top plate ready to be welded on the tube.

Top plate with baader heq5 pro mount adapter test fittingTesting the fit 🙂

Base plate welding for the pierWelding the M30 threaded bars to the base plate. By Tom of course!

Pier top finishedThe pier is ready

Finished pier top to bottom viewAnother view of the finished pier.

Transporting the pierThe pier and the base plate ended up weighing some 75kg, which we had to haul in the 5th floor (rooftop) by the stairs since there is no elevator yet 😀

Ready for the fumes!Oil paints, 2 part epoxy glue, white spirit solvents and in general chemicals require some kind of protection. Thus the mask for the fumes and the glass (i am nearsighted(myopia) but they work as protection from splinters, most of the time at least..)

Materials for the gluing and paintingVarious assortments for gluing, sanding and painting of the pier

Two-Part Resin Epoxy Glue preparation2 part epoxy cement. Yes, this stuff is from hell so do wear gloves, berathing mask and general protection.


Base plate "tagging"The base plate orientation was tagged with white spray the previous night after a rough polar alignment.

IMG_20150604_225232Finally ready after two hands of oil painting, sanding in between and gluing the base plate to the floor. By the way the 2 part epoxy resin turned out to be massively better than its description. After allowing the 24 hour requirement for it to be properly cured i would need some kind of demolishing device to remove the base from the floor!

Mad design skills for the eyepiece - accessory holderSuper design skills at work here in order to make the blueprint for the holes and cuts needed on the plexiglass accessory tray.

Finished pier ready to receive the HEQ5 PRO mount head


Finished pier ready to receive the HEQ5 PRO mount head with controllerFuture upgrade plans include building a proper astronomy shed – observatory around it but that will have to wait for a while 😀

Kudos to Tommy, for the help!