Blasting cabinet mods

Here is my blasting cabinet in operational condition albeit still on the floor in this picture. The small rectangular box contains about a litre of pantyhose filtered glass beads ready for use in the small blasting pen. The blasting pen is the one with the long and colorful hose in the middle and it has a small cup that holds the blasting media.

The original blasting gun was supposed to be installed with a small female connector in the right hand side panel so that there would be a G 1/4" female thread for a pipe connector. But as I'm not going to use the original gun but the blasting pen and I want a small air gun in there also for cleaning, I made a small splitter block from aluminum. The splitter block has two female quick connectors to attach the pen and the gun. The splitter has G 1/4" threads for the quick connectors and one cross drilling that I plugged from the end with an R 1/4" plug and pipe connection glue.

The air gun is from Biltema and provides very good adjustability as the trigger lever is long. It also happened to have the dangling hook in an otimal place just by coincidence, as I found out that it fits perfectly loose to the M4 screw that holds the air filter in the cabinet and is in reach of my hand while working. The hose for this air gun I liberated from the original blasting gun as it is quite thin walled and very flexible, so it is easy to maneuver inside the cabinet.

The inlet to the splitter block comes from the compressor with a hose that has a female quick connector in the end that fits a male quick connector. This is attached to an elbow joint that is going through the cabinet wall to the splitter block and keeping it also in place. The elbow connection saves me some lateral room as it comes out only about 30 mm from the side of the cabinet versus about 100 mm that it would take with the quick connector & hose coming in horizontally.

Blasting cabinet

I bought a blasting cabinet from Biltema (article #15-377) for 159 EUR. The cabinet is quite small so it fits my workshop well, as it is more than enough in size for my parts. My intention is to use this with the silent air compressor I built earlier, but I'm going to use a small blasting pen with this cabinet to keep the air consumption low. My blasting media will be fine glass beads as I want to have a nice finished surface on my parts and one lock related project needs this also.

And as with all things that I carry home, it happened once again. I get the box inside, close the door and turn around and the Quality Inspection Team is all over the place. Yup, that's my other cat, enjoying a new toy. Well, at least they get the box afterwards as they love to play and sleep in them :)

The box contained all the parts neatly packed and properly shielded with lots of bubble wrap. I pulled all the essential small parts out front to take this picture. In here you'll see the V-bottom of the cabinet, the gloves, the supplied blasting gun and four nozzles, the lamp and a power source for it, instructions manual and a bag full of nuts & bolts. Notice the grey foam around the V-bottom, this was preinstalled but I was not thrilled of it and the next pictures shows why.

Here I'm applying very liberal amounts of butyl sealant with a caulking gun. The sealant was a 300 ml tube from Biltema for 3.99 EUR and the gun also from Biltema for 2.99 EUR. The butyl sealant is good as it remains elastic and kind of rubbery when it hardens fully (around 1-3 weeks). Downside is the enourmous force needed to squeeze it out of the tube, as it is very thick.

The sealent begans to surfaceharden after about 20 minutes so there is plenty of time to install the parts and screw everything down. In the picture I'm just installing one of the sides to the V-bottom after applying the sealant. You can notice that I removed the original foam seal from the V-bottom. The reason is that I didn't like it and I had a tube full of this butyl sealant that I could install instead. I wanted a blasting cabinet that would not blow the blasting media all over my room from the small holes that would have been left in the corners and joints where the bolts are. Applying this sealant to all mating surfaces provides me an "airtight" blasting cabinet and helps to keep noise level and cleaning down.

The only difficulty I found installing all the parts was with the gloves. I couldn't keep them in place with only one hand while trying to fit the compression ring around them with the other. Finally I figured out that I could put the ring ready on the glove, fold the gloves edge around the ring and then install it in the cabinet. Worked well and got everything assembled. In the picture you see the original gun and its nozzles and the small 12 V transformer for the interior light. This is a nice safety feature as there isn't 230 VAC inside the cabinet. On the right hand side in the upper back corner there is a small yellow air filter that lets out the air but keeps the blasting media inside and also drops down the noise somewhat.

Although the cabinet has its own feet, I'm not putting it on a table but will make feet for it instead and write about them and one other mod I have in my mind.

How to change gears in C4 lathe

I have to admit that this new change gear system SIEG has done is just wonderful, as the change can be done in a minute and easily without any modifications nor hard to reach places.

First open the small socket head cap screw from the front to get the gear cover open. Inside you'll find the regular arrangement of gears. In this picture I have the new gears ready and the BC-gear pairs mounting axle dismounted and all the necessary tools to make the change.


Put the sleeve with the key on the axle, then the small washer and thread the T-nut on the axle a little. Slide the T-nut behind the geartrain holding arm and the washer on the front side. Snug up the axle with fingers.


Slide the B gear on the sleeve and then the C gear after it. Now move the axle so that the C/D pair engages properly and tighten the axle with a 7 mm wrench. If the A/B pair gets in the way or is not engaging, open up the socket head cap screw in the lower end of the arm, located just behind the D gear and turn the arm down a little. When you have C/D engagement correct, move the arm to engage A/B properly and tighten the arms screw.

As a last operation drop the cutout washer on the axle and thread the locking nut in place. Even fingertight is enough, but I'll usually snug it up a little bit with a wrench to be sure it doesn't open up under vibration.

This is so easy and fast to do than on the older C2 lathe that I could change the gears just for the fun of it! :)

Bigger tools to the C4 lathe tool post

The original tool post that comes with the SIEG C4 lathe accepts up to 13.8 mm thick tool shanks, but the maximum tool height to axis of rotation is only 10 mm. I think this a place where SIEG should make a change to their lathe as the lathe has enough power to use bigger tools. Only needed operation would be to make the tool post 2 mm lower.

My own way of modifying the tool post was to use a surface grinder to take off 2,00 mm from the bottom of the tool post. Because the tool post goes over a small shouldered bolt in the compound rest, the bolts shoulder had to be turned shorter. I took about 1.6 mm off of the length of the shoulder in a lathe and chamfered the edge.

I bought a DNMG insert holder from eBay that had a 20 x 20 mm shank and wanted to use it in my lathe, so again had to modify it to fit my tool post. I tried my best to search for 12 x 12 mm shank DNMG insert holders, but could not find any, so the 20 x 20 mm shank had to be bought. At the same time I also bought a 10 piece package of DNMG 110404 NF inserts. The nice thing with these inserts is that they are negative inserts, meaning the insert can be used four times and for me this means 1 EUR per insert edge, so very cheap.

To minimize measuring and setups I used a surface grinder to knock off all the material needed from the insert holder. First I measured that I could take about 5 mm from the bottom safely without messing with the insert retaining screw. Then the remaining 3 mm from the bottom I took so that I created an edge to the holders bottom as can be seen from the photos.

Last operation was to take 8 mm from the backside of the holder so it wouldn't hang so much out from the tool post. This was easy and fast and the last operation I did was to chamfer all the sharp edges with a file. The shank material was hardened, but filed quite okay.

Last thing to do was of course test this new tool with the new tool post mod. The tool sat very well, about 0.1-0.2 mm under the center of rotation as I checked it with a dead center mounted in the tailstock. By the way, it is a good practice to keep something in the tailstock taper as it prevents chips from entering it.

For the test I used RPM of 600 for a 60 mm diameter scrap piece. This gave me a surface speed of 113 m/min now that I calculated it. I usually aim for about 120 m/min minimum if the steel is nothing special. The feed was 0.15 mm per revolution. Depth of cut was 1 mm and the lathe happily purred away throwing short painfully hot deep blue chips. The finish was very good, considering a feed 0.15 and an insert radius of 0.4 mm.

I'm very happy of this tool post modification as it means that I can finally use the lathe :) I'm still going to buy a quick change tool post, but this will do until then.

Test chips with the C4 lathe

Two words: Eye protection. Really, this thing makes chips fast and not just bogging sounds like the old C2 lathe I had. Here is a nice comparison photo of the old C2 lathe that I had and the new C4 lathe that I now have, both mounted on the same table in both pictures. Have to find a place or build a stand for the drill press, as it is a good thing to have when the mill is reserved.



I whipped up a quick test to see how much better this new C4 lathe is compared to the C2 that I previously owned. I found a piece of steel scrap from my material box that measured about 60 mm in diameter. The only tool that I had ready for this test was an old but sharp HSS turning tool measuring 7.5 x 7.5 mm, so I had to shim it up 2.5 mm to get to about center height.

I used an RPM of 150 which means about 28 m/min surface speed. The recommended speed for HSS in steel is about 25-30 and with coolant, but I did this test dry. I touched the workpiece and dialed a depth of cut of 1 mm and engaged longitudal feed. The feed was 0.15 mm per revolution, so something between a roughing and finishing cut.

As the tool came to contact with the steel bar I could hear a small bogging sound in the RPM but at the same instance the motor grunted more power and chips started to fly around. Hot blue chips on to the table, the floor, over me and that was the point I withdrew the cross slide and cut off the feed. Just..wow! On the old C2 lathe steel would have been a problem and basically anything with a 60 mm diameter, but this machine barely noticed that there was something in the way of the cutting tool.

The other test I conducted was a drilling test to see how big drill bit can be used safely in to solid steel workpiece. The tailstock has a #2 Morse taper and biggest drill I know for that size is 24 mm in diameter, so I used that size drill bit. The tailstock ram is better than in the old C2 lathe as it can hold a Morse taper with the tang in place. But there is no slot in the end of the ram for the tang to go in to, so there is a risk that a little bit loose tool can turn in the taper.

I set the RPM to 350 to provide about 28 m/min cutting speed and I had no pilot hole in the test piece. The tailstock tended to come loose from the lever lock but when I kept it in place the drill went in nicely and the machine power was more than adequate to drill the hole.

After drilling I noticed that the tailstock ram was a little bit stiff and revealed that the small M6 grub screw that acted as a "key" was a little bit bent. No wonder under that load, but have to put a new screw in there.

I can't wait to get my new Multifix Aa type quick change tool post and to modify the DNMG carbide insert holder to a 12 x 12 mm size, as it originally is 20 x 20 mm. I already milled and surface ground the height to about 11.90 mm, but the width is still to be done. The turning insert holder cost me 68 EUR plus 36 EUR for 10 pieces of DNMG 110404 inserts. This holder I bought from the German eBay seller cd-tools.

Frank J. Hoose Jr. at mini-lathe.com did also a nice review of this C4 lathe which you might find interesting.

Pros & cons of the SIEG C4 lathe

I have had the SIEG C4 lathe for a couple of weeks now and although I haven't had the opportunity to turn anything to chips with it yet, I have seen quite many good and not so good things in it while disassembling, cleaning and assembling. My comparison level is basically the older C2 lathe and the "real" lathes that I use at work (TOS and one huge chinese machine).

Pros

• Weight is a nice 94 kg and comes from the bed casting mostly. This is a good thing to have, except I would list it as a con when I have to lift it to the workbench or move it around. The size of the lathe in terms of travels didn't increase that much from the SIEG C2 lathe, but the weight really jumped from the 37 kg mark, so this really is a big jump from SIEG.
  
• The 1000 W brushless motor really provides tremendous torque versus the C2 lathes 250 W DC motor that had brushes.
• LCD dislay for RPM reading
  
• Leadscrew cover keeps the chips out of the screw and also protects fingers, as the screw has a keylot along its lenghth and it has quite sharp edges.
• Leadscrew bearing blocks and the apron both have hardened pins to lock them in certain place and this helps keeping things in proper alignment. More points from using pins that have a threaded hole to help yanking them out if needed.
• Tailstock has a lever operated locking mechanism, very fast to use especially when drilling deeper holes than the quill movement is.
• All metal change gears are nice and have precise holes that allow smooth sliding fit to the axle ends when installing, unlike the C2 plastic gears that had an undersized hole in them.
• Metal gears in the headstock transfer more power than plastic ones and will also handle more loading conditions without chipping a tooth.
  
• Oiling ports everywhere: Apron, carriage, tailstock, spindle, gearbox axles, leadscrew bearings, cross slide, headstock etc.
• Split nuts in the compound and cross slide movements provide a mean to adjust the backlash to a minimum. In basic turning operations the backlash doesn't have any effect on anything and in some instances it is a nice feature to have.
• Carriage handwheel has a graduated collar that measures 0.5 mm between lines. Very good update from the C2 that had no kind of way to get Z-axis measurements.
• Carriage handwheel can be disengaged by pulling so that it won't rotate while power feeding.
  
• Cross feed helps hands if turning larger diameter parts.
• Feeding directions are logical in the sense that when the Z-axis feed is towards the headstock, the cross feed is towards the center of the part.
• The changing of gears is easy due to the B/C gear arm that is very quick and easy to adjust.
  
• Total indicated runout of the spindle MT3 bore is 0.005 mm or less
• Total indicated runout of the chuck index is 0.005 mm or less
• Total indicated runout of the spindle face is 0.01 mm or less
• The tailstock ram accepts full size #2 Morse taper tools unlike the C2 lathe that required the tang to be cut off to utilize the full movement of the ram.
  

Cons

• Spindle and leadscrew relative rotation directions are fixed. There is no change lever like the C2 had, but then again, how many times that was needed? Personally I never used it.
• Cross feed speed is sssslooowww compared to the longitudal feed at the same change gear setting. Basically if the longitudal feed is 0.1 mm per revolution, the cross feed is only about 0.032 mm.
• The change gear cover box doesn't come off unless the electrical cabinets panel with the small fan is removed first, as the panel screw heads will be in the way. And removing the little screws is dificult because the gearbox cover is in the way.
  
• There was either sand mixed with heavy oil/lube or some sort of course lapping compound in the headstock gears that was causing huge noise and was a possible wear inducer.
• Almost every electrical wire is either blue or black inside the machine. Not good when trying to figure out where some wire went, but at least some wires had labels on them.
• The beeper is plain annoying. Beep when you turn the machine on, beep when you push the buttons. A jumper on the PCB for disabling it would have been a nice feature.
• The safety interlock in the chuck guard is not logically done: If you don't push the microswitch (like remove the whole shield), the machine runs fine. But when you push the switch, the machine shuts off.
• The tailstock can bump in to the gib screws of the cross slide. This could be prevented by installing a small screw in front of the tailstock.
• Painting has been done for a half-assembled machine, as there is painted socket head cap screws, some not painted, some parts painted that should not be (like the carriage gib "paws") and the paint also flakes off easily from the cast iron surfaces.
• Carriage gibs don't have counteracting screws or locking nuts for good adjustment.
• The cross feed dial is reading radius and not diameter as would be useful.
• The cross feed dial numbers don't correlate to any "real" values, they are just for counting.
  

All things considered with the relatively low price of 1100 EUR that I paid for this is a very good investment and the SIEG quality has gone up since the C2 lathe. Personally I can suggest this C4 lathe to others and say that I very much like it.

Silent air compressor

For a long time I have wanted to have pressurised air available, especially for glass bead blasting of machined parts. The main reason I haven't just bought an air compressor is that they are loud as a jet engine, usually in the order of 85-95 dB and that just doesn't cut it in an apartment complex.

About a year ago I stumbled upon articles in the internet of how to use a freezer or fridge compressor to produce compressed air silently. The only drawback is low air output volume, but my need is occasional and very little, so this fits for me.

A week ago I was able to obtain a working compressor out of an old freezer. This was an old ZEM compressor with 110 W of power and it runs from 230 VAC 50 Hz supply. The best thing is that it was from a freezer, as these are usually more powerful than compressors from fridges. The compressor had its original oil still in it, so I poured it in to a junk oil container and replaced it with a regular oil meant for automatic transmissions. The only requirements are low viscosity and that the oil is of mineral variety.

These freezer compressors are able to produce enormous pressures and also vacuums, so care must be taken that the system is able to withstand the pressure. This usually means a pressure switch that cuts of the compressor when the pressure reaches a set upper limit and starts the compressor when the pressure drops below a set lower limit. Also an overpressure valve is needed, as it vents if the pressure switch doesn't switch off the compressor.

To have a big supply of air for some time the compressor needs a pressure tank after it. This can be an old carbon dioxide extinguisher bottle or gas bottle that is rated for the intended pressure. There is also a need for the pressure switch, pressure regulator, connectors, piping, oil/water catcher and air drier. If you have to buy everything as new, the total will cost probably around 100-200 EUR plus all the work needed to assemble everything.

This is the reason I thought of buying a brand new compressor unit and just replacing the compressor unit with the freezer compressor. So I spent 89 EUR to buy a Herkules brand compressor from Bauhaus, as it was the cheapest I found that had a 24 liter pressure tank. The original compressor unit fills the tank in about 2 minutes from 0 to 10 bar, but produces an ear breaking noise of 97 dB at the same time. Not good.

So I started disassembling the unit to get the original compressor out and to take measurements of the pipe size used so I can make or buy a proper sized fitting between the pressure container and my freezer compressor. It was quite easy to just unscrew the plastic cover to reveal the compressor unit, but the Abiko connectors to the power switch didn't want to come off so they got a quick treatment from pliers.

After removing everything not needed, I was left with a tank, a one way valve, a pressure switch, overpressure vent and pressure gauge with an adjustment valve. The output is a 1/4" female quick connector and the input to the tank is from the end of the one way valve that has G 3/8" male thread.


The freezer compressor had a 1/4" OD copper tube as its output, so I bought a hose connector that had a 1/4" hole through it. From this I hacksawed the hose connection part off and after cleaning everything, I soldered this to the compressor output tube. To the one way valve I rolled few turns of PTFE tape and screwed on a G 3/8" -> 10 mm hose connector. This way I can attach the compressor to the tank with a small length of hose and avoid induced vibrations to the tank and also avoid messing with rigid tubing and bending.

The pressure switch was factory set to have 10 bar upper limit and 8 bar lower limit. I plugged the modded compressor to the wall for a quick test and started a timer to see how long it takes to fill the 24 liter tank from 0 to 10 bar. The pressure rise was slow but steady and finally after 24 minutes the pressure switch turned the compressor off. This means that the compressor can provide about 10 litres per minute. The 0-5 bar rise time was exactly 10 minutes.

I was a little bit doubtful if the freezer compressor could start against pressure, so I blead the tank slowly until I heard the pressure switch click on at the 8 bar marker. The compressor immediately started to purr and building more pressure to the tank. I timed how long it took to see how much the air output volume would change from the first run as this was against pressure. It took 4 minutes 50 seconds until the compressor shut off, so against pressure the compressor can provide about 9.93 litres per minute, which doesn't differ from the 0-10 bar rise time.

The compressor temperature climbed to quite warm during the half hour test, meaning I could not keep my hand on it for long. I'm quite sure my air need is so small that this will not be a problem as I can switch the compressor off when I have pressure in the tank, but I could add a small 230 VAC fan to blow cooling air over it.

Of course mounting the freezer compressor meant that I had to fabricate some sort of plate that attaches to the tank mounting holes and that has mounting holes for the freezer compressor. I used a proper sized piece of aluminum plate that I countoured with a CNC mill and drilled and threaded for M6 screws. I used the freezer compressors own rubber feets to isolate vibrations from the unit to the rest of the system. In the rear end I also installed a small water separator unit that is screwed to the plate and inside the plate is an 8 mm passage for the air. On the back side there is one electrical connection to the pressure switch, which is wired in series with the fridge compressor and shuts it off when there is 10 bar in the tank.

So how silent is my silent compressor? Well, I can just hear it running, sounds like a fridge humming its things. Yep, beats the so called "silent" compressors they advertise in hardware stores with about 68-70 dB sound output.

Added 06.01.2011: I bought a small Simota brand air filter that had a connection for a 9 mm diameter tube. This was probably meant for some RC car or something, but works wonders in this application and totally eliminates the small intake sound of the compressor.

I also had an idea for a decal to replace the original "Herkules" tape and so I used 5 minutes with KolourPaint and printed off a nice new decal and attached it (poorly) with a piece of tape meant for covering books. The word "Perkules" is a kind of twist from a Finnish curse word "perkele" and the original brand "Herkules". The word below it is my own drunk misspelling of the word "kompressori", which is Finnish for a compressor.