I’m very proud of my anti-backlash five start acme nut

I know it’s beautiful isn’t it? I’ve been using and researching acme screws for about ten years and at one point had access to a fancy acme tap which has since gone missing and that’s a shame as it cost a few hundred dollars. This tap would have allowed me to create the same style anti-backlash nut as shown above but in a more solid material like brass or steel.

Thanks to some kind thingiverse user I found a cad model for this exact thread and I used it to 3D print a few hex nuts just to see if it worked. When I printed and then threaded the nut it was a bit more than surprising that I could actually print a thread, mind you a 1/2″ acme thread is about as course as you’ll ever see this side of ship or bridge parts. 

In the cad image above you can see clearly how the threads on a five start acme nut work. The springs apply tension to keep the nut from wobbling on the threads so the small nut is located from turning by the 10-24 bolts. Better hardware would be some kind of shoulder bolts and I will keep my eyes open for them but for now the tiny threads pose no problem for the amount of travel required here.

The test fixture pictured above allows some torque to be applied and the deviation measured by a dial gauge (not pictured, sorry) Meccano is handy for quick fixtures.

Here’s the nut mounted to the side of my Y axis gantry.


Another shot of the gantry.

Video of Acme screw in action.

If you’d like to see the CAD files check out my Thingiverse page.


Building a New Basement Stair


Newly completed stairs, view from old doorway.

We had initially planned on only painting the den and changing the carpet but the carpet place had a big sale on what we wanted and a special promotion for free installation so we got a quote. The price seemed good and we decided to have the stairs recarpeted at the same time since it was almost as bad as the den. The installer’s rep came out to inspect and do a final measure, he turned out to be a really good guy and gave me a number of useful tips from his years of being an installer when he was younger. One tip was for me to remove all the old carpet and padding and have the floor ready when the guys got there. He said that they charge extra for the time to do this and also charge a disposal fee for what they take away and if I found anything that needed to be fixed I could reschedule the install until after the work was done but if the guys came out and found anything that would stop the job I would be charged for the time they wasted.

The den is on a concrete floor so removing the carpet was as easy as cutting it and rolling up the pieces. My garbage took the carpet so the total cost for this was zero. Next I started to remove the carpet from the stairs. Under the carpet the first thread had a huge crack in it, then the second and now the third was found broken. At this point I stopped and had a good look at the rest of the stairs.


Old landing, repaired once.

The stringer was sitting on the landing with no support and at the top of the stringer was two huge cracks so the stringer was no good either. I had remade that landing when we moved in as it rocked and flexed when you walked on it. The person who built it used 2x4s and two pieces of plywood for the top but did not add a support where the two pieces joined, that made the flex and the rocking was caused by the nails pulling out and twisting. You can see my quick fix uses 4x4s and carriage bolts.


Ruthie loves to be in the picture

You can see the two cracks here, the photo makes them look better than they are but every time I walked these stairs I could feel the stairs moving and making noise as these cracks opened and closed.

Starting the new stairs: The web and youtube were very helpful in planning the new stairs. One of the first things I found was recomendations to consult the local building codes. I did this and found that the old stairs had too high a rise and the stringer were made with wood that was too small. In my area the homeowner is allowed to make “home improvements” that don’t comply with local code but since I had to buy all new material to build this stairs I used the code as my baseline and in most cases I went above the minimum requirements.

During planning I asked my wife if she wanted anything changed on the new stairs and she complained that she was afraid she would hit her as the bottom landing was too near the ceiling. I hadn’t noticed this but she was right and the space was also smaller that the requirement in the code. To change this I would need to shorten the top landing and move the stairs further away from the ceiling. This move would require that the door to the garage be moved to the den. That’s now a big deal so I slept on it for a few nights.

All the homes in my neighborhood were made by the same developers and quite a few of them are very similar in design to our home so I have a keen interest in them and always try to see what they have done and it was noticed that all of them had the garage door going into the den and not the stairs like mine. I never liked that door and how it blocked the stairs and what a pain it was to bring anything in especially groceries which you do often.

Back to the hardware store and a chat with the boys at the door department. They said I need a firedoor and spend a few minutes showing me how it should be mounted. At home I find that it’s not a firedoor and it was the wrong frame for the opening and it was mounted wrong and that wrong mounting caused the door frame to crack all around the door. So not only is it a tiny door in the wrong place but it’s the wrong door and they broke it installing it! Great.

New firedoor costs $190 and takes two weeks, I’ve ordered the carpet but they don’t schedule the install until it arrives so I can put them off until all the work is done. I order the door and start the stairs. Youtube videos show many ways to make a staircase, I have to pick on that I feel I can build with the tools I have. One guy says you can make the whole thing with just a handsaw and a chisel and I’m sure he’s right I’m just not that guy and keep looking.


This is the first cut I made, it allows the mockup to sit flat on the floor like the finished product will.


Here I’ve made a mockup of the stringer angle from the height and length needed in the basement, this way I can make sure everything is correct before cutting anything.


You start by clamping a piece of wood on a square that has been set up to show your thread length and your rise. You then transfer those dimension to your stringer in pencil to make sure everything lines up. I did this many times making adjustments each time, a good tip I found was to use a different colored pencil for each try.


This full size drawing on graph paper allowed me to easily transfer the marks on my stringer to the template boards.


To build the stairs I chose a method that uses a router and four templates, one for the thread and one for the riser on both sides. You can do it with just two but it is easier to accurately cut two squares than to get an “L” shape perfect so I went with that.


Above is one thread template, you can see how I notched out the end to get the contour of the bullnose on the thread. The piece of wood under the template is one of the guides to keep the template on the same angle for all the treads. On the right is the riser template, you can see that I’ve been cutting here, you just line up each template and cut out the slots and repeat for the entire length. It took me about a day to cut each stringer.


Here you can see how once I get the markings perfect on one stringer I transfer them to the other. This requires that you move the reference on your square to the other side (in background).


I don’t have any shots of assembling the staircase or of the hardwood wedges I had to cut to shore up everything nice and tight but suffice it to say it was the hardest part of the job. The wedges were cut from an oak shelf bought for this purpose, you have to cut them with a slight variation as each one needed to be slightly different. My building code says you need to use long and large nails to hold the threads as they won’t break off like screws will but there is an allowance to use a screw to aid in assembly which is what I did. I also used glue and construction adhesive. As an extra and likely overkill point I doubled up on the riser boards with one blind riser and a custom one cut for each step that is attached to the front.


The tops of the stringers were cut off after a test fit since I wanted a perfect fit here.


The bottom thread is open because the last staircase was too and the cat liked to play in there so we grandfathered it in. The stringer sits on a very large plank and is attached with carriage bolts, if this plank were to become damaged from moisture it can be replaced without removing the stairs. The landing is also easily removable because there is a floor drain underneath, it’s heavy but you can move it.

It’s been installed about four months now and we’re still very happy with the results. The new door is in and all the drywall has been repaired and painted. We love the carpet too. Next I’ll put up a hand rail and it will be finished. We’ve saved a ton of money thanks to having some basic tools and using youtube and our local hardware store.

For my next post I’ll be documenting the installation of a pretty large assortment of LED lighting and dimmers.




Designing a crossover exposes more faults than solutions

I would like to discuss my results of working with passive/active crossovers that I had while trying to upgrade my studio monitors. Studio monitors are used in the recording studio to provide musicians with a feed of the sound or to amplify an instrument, they are usually not used for mixing or in the control room.


All of that means these are normally a large speaker capable of competing with other instrument amps and loudspeakers so efficiency is important. Mine are a three way design with a 12″ woofer, a sealed mid driver and a large compression horn. They were hand built using commercial sound drivers, the cabinets are thick birch plywood with braces and covered with Ozite and chrome corners with recessed handles and large rubber feet, sturdy and tough but certainly not what you want in your home.


The sub-bass cabinets were added after I built the 3 way cabs when it was found that there was no way I was going to get both a flat response and low enough bass response. These cabs are from the 1950s and originally housed fine German full range high-fi speakers. If you look closely you can see the baffle folds around at the sides and is vented along the entire vertical surface of the cabinet. This design is perfect for my sub cab and was one of my better craigslist finds. I had to recut the speaker opening to fit the beefy die cast basket.

The speakers always sounded good to me but after a session with some talent that continually produced a rather harsh feedback both my horn drivers were blown and I had to open them up. The JBL diaphragms were easily replaceable but I noticed that the tiny crossover looked barely capable of 50 watts and I had the cabinet attached to a 450 watt Citronic/Lantek mosfet amp.


Crossover plot and modified crossover

Years ago I acquired a pair of beefy McIntosh three way crossovers and I used these as a starting place before modifying and upgrading them for my use. Here is the schematic and simulation,


McIntosh crossover schematic

As a control I took two three-way active crossovers (one dbx 223 and an Ashly XR70-12, substituting one for the other) and three amps for the first channel and for the other channel I used the modified McIntosh crossover and a single channel amp.

Much to my dismay, after many hours of substituting and upgrading components I could never get anything that sounded as good as the tri-amp system and the flexibility of having all the multi amp controls sure beat all the soldering and expensive caps and chokes I was going through on the McIntosh crossover. Luckily I was able to get a few caps at a very steep discount and a friend happened to have a few high end chokes I was able to test.

The more I added to the circuit to achieve the response I desired the more the crossover sucked up wattage. Initially I was using a 60 watt amp for my testing but as the crossover grew so did the power requirements and the overload lamp started to light at even low volumes. Now I know why there was such a huge heat sink on that crossover, who wants to pay amp dollars just to heat a resistor?

I finally gave up on modifying the crossover and just built a tri-amp system. My studio monitor system now contains a Rane MA 6S 6×100 watt amp with 4 channels bridged driving the woofers and the 2 remaining channels on the mids. An Ashly SRA with 60 watts is driving the horns and believe it or not I’m using a Behringer CX3400 three-way stereo crossover. Its my first Behringer product and for the money (way too good of a price used at GC) is a screaming deal and has even more control and more modern circuits than the more traditional pro units I was testing with.

Behringer CX3400 Super-X Pro Crossover 3-Way Stereo

Not only does the CX3400 have limiting that will protect those horns that had fried but it also uses the new math theories for crossover design and some advanced features like adjustable time delays for phase alignment and CD horn equalization which I needed but lacked before. According to the reviews I’ve found it offers all the features of units that cost five to ten times as much as I paid for this one.

I was always down on Behringer due to a mixer I used years ago where I leaned over the large console and my elbow left a large dent and some of the faders stopped working, this new piece looks very solid but I’ll keep my eye on it and I’ll let you know how it performs over the long run.

The only real drawback to me is I now have to maintain non-standard speaker cables with 6 leads in 8 pole Speakon connectors that only fit this system. This system has been a real pleasure to use, so much so that I find myself often in front of them for reviewing material and even some musicians who had no idea they were modified commented how much better they sounded.

The rack ready for testing

The rack ready for testing. I’m only one rack space taller than the old setup but overall its lighter and infinitely more flexible.

I realize my system is a bit over the top and may not appeal to audiophiles but I’ve noticed that pretty much all of the control room monitors have gone bi-amp or tri-amp. Even my audiophile friend who has a rare and huge bi-amped Infinity IRS system wanted to borrow my crossover.

UPDATE: 11/7/13: Small rack located for rig

6 way power rack

Just a little wiring job.

Found a nice home for my monitor power rack and wired everything up nicely. I’m still short two Phoenix connectors to bridge the amp to drive the woofers to their potential but that will only take swapping one wire and hitting one switch so it will have to wait for the next Mouser order.

Notice how much hand wiring is required with this gear, the Rane is really designed for installation use so it only has hardwire connectors and the Ashly is only 1 7/8″ tall which reduces the cable choices. I used the terminal strip on the Ashly to avoid the 1/4″ jacks which would have also required a custom cable it’s just less parts with the screw terminals.

A closer look will reveal an extra Ashly crossover tucked in there, it’s not doing anything as it’s sort of semi retired. This crossover was used with a keyboard monitor consisting of a wedge cabinet that held a beautiful Sammi Coaxial Speaker and powered by a BGW 250C. I have them listed on ebay but they really are a beautiful setup for keyboard monitoring and a lot easier to carry than my new setup.

UPDATE: 10/24/16: Finally found photos of completed rig. (they were hiding on an unused USBstick)


Power amp harness

Above is pictured the final wiring harness for the 8-way speakon connectors. The silver XLR connectors are paired with the green Pheonix connectors which supply the inputs from the crossovers to the four channels of the Rane amp. The black XLR connectors are from the outputs of the Lantek, some amps used these on the output and I’m not a fan of using the same connectors for input and output so I tried to install Speakon jacks but there’s not enough room! I did search out connectors with the largest lugs on them but I’m still not happy.


Power amp rack in service

This is how the amp rack looks now after being in service for about two years. Underneath you can see the two 8-way Speakon cables plus two pairs of midi and a silver USB over ethernet cable. All the power cables are routed behind and along the wall far from the audio cables. I’ve spaced out the gear to reduce heat build up which worked as the fan in the bottom amp hardly ever goes on now.

UPDATE: 31/10/2017:

3D Printed Speakon Panel 

Some rearrangement of the studio required the amp rack to be moved more to the rear of the studio which caused the speaker wires to be stretched out fully and still was short a foot or two. The solution was to extend the breakout leads and move the Speakon connectors to the front of the rack.

If you need a handy 2 connector panel that holds 8 conductor Speakon jacks just follow this Thingiverse link.