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MachinistBlog.com

Plans, projects and how-to's for home machinists

Review – $40 QCTP for 7x Mini-Lathes

This is a review of a very inexpensive Quick Change Tool Post (QCTP) set for 7x mini-lathes that can be purchased on Ebay for about $38 (including shipping).  It is considerably less expensive than similar size QCTPs that you can find on LittleMachineShop.com and Amazon that cost about $135 to $155 plus shipping.

I purchased it because the cut-off blade holder for my 10-year old A2Z CNC QCTP had broken and I needed another one ASAP.  I didn’t have time to fix it and I couldn’t buy a replacement because the company has gone out of business.  My set was on loan to the SparX 1126 FIRST Robotics Team, where I am a mentor, and it was getting heavy use because we were in the middle of the build season.

So, when I came across this cheap QCTP set on eBay I decided to take a chance and buy it for the team.  The same set is sold by many eBay vendors and I chose this one and paid a higher price, $45, because they were promising delivery sooner than most other vendors and the seller has a high rating.  It was delivered six days after I ordered it.

It’s manufactured in China and it comes with four tool holders – two identical holders for turning and facing bits, a ⅜-inch boring bar holder and a holder for ½-inch cut-off blades.  The tool post is made almost entirely from hard anodized aluminum and the tool holders are made of steel.  In comparison, the $135 QCTP that Little Machine Shop sells for 7x lathes is made entirely of steel and it includes an additional holder that can knurl in addition to hold another tool bit. Continue reading Review – $40 QCTP for 7x Mini-Lathes

Rear-mounted Parting Tool Holder for Sherline Lathe

This is the rear-mounted parting tool holder for my Sherline lathe.  It’s based on a design that’s been around for decades and I made it about 12 years ago, before Sherline offered one for sale. It is just a block of 6061-T6 aluminum and it cost almost nothing to make. Further on you’ll find drawings that will help you make your own. The design could probably be adapted for 7×10/12 mini-lathes, which are notoriously bad at parting-off.

Yeah, I know its beat up and ugly but it is extremely solid and functions perfectly. As you know, a rear mounted parting tool pushes the carriage down instead of raising it up so rigidity is markedly enhanced. My parting tool does not chatter, dig in, or deflect. It cuts cleanly in all materials I have used it on, at speeds averaging 2-3 times normal turning speeds.

The main features of the tool holder are

  • It accepts all 1/2-inch tall P-type blades, mounted upside down.
  • The bottom of the slot is on the exact centerline of my particular lathe. This allows the tool to be extended however far I need while still remaining at centerline. Canted designs do not do this. The Sherline OEM tool holder may not be on the centerline either so a shop-made one is a better option.
  • There is a ledge on the bottom of the tool holder that automatically aligns the tool perpendicular to the work. A single screw locks the tool to the carriage in a few seconds. The ledge eliminates the possibility of movement, even under very heavy loads.

Inverting the parting tool does several things

  • Improves geometry. Instead of being a zero-rake cutter an inverted tool has back rake, which assumes the importance of side rake on a turning tool. This not only reduces cutting forces but also greatly improves chip ejection from the cut and thereby also reduces cutting temperatures. Furthermore, the 5-degree side rake on a P-type tool also narrows the chip, improving chip ejection even more.
  • Improved oiling. On an upright parting tool the chips are piling up on top of the blade and carry much of the cutting fluid away before it even gets to the tip. With an inverted tool the oil gets to the tip first, further reducing cutting temperatures and improving both accuracy and finishes because the cut is no longer dry.

So, you have greatly increased rigidity, reduced cutting forces and cutting temperatures, improved oiling, and the ability to cut at higher speeds that leads to improved accuracy and finishes. With all of this I cannot imagine why a guy wouldn’t rear-mount a parting tool!

I also believe the improved geometry allows a blade to cut a larger work piece than expected. A P1N blade is usually used for work up to 3/4-inch OD but I use mine on work up to 1-1/2-inch OD, double what you would expect to be able to cut. I do alter the angle at the nose of the tool; I use 7 degrees instead of 5 or 10. I have found edge life to be greatly improved, while still clearing chips easily.

Here is an example of a cut made in 12L14 mild steel. The OD is 1-1/4-inch at the cut. Depth of the grooving cut is 5/16-inch and I made two cuts side by side to allow my turning tool to fit in there. Speed is 1200 RPM and I purposely extended the blade about 5 times more than needed for this depth of cut to see if I could induce chatter – there was none – note the finish inside the groove. This part was later parted off about an inch from the chuck at the same speed and came off cleanly. I assure you that I cut like this all the time, in all sorts of materials.I set cutting speeds based on how the feed feels. The tool should cut freely and easily but allow me to feel the tip in contact with the work while feeding at a pace I can keep up with comfortably. Because the tool cuts so well there is little fear of digging in or chattering so speeds and feeds are much higher than you would expect. Continue reading Rear-mounted Parting Tool Holder for Sherline Lathe

Smithy Granite Clutch and Driven Pulley Bearing Replacement

New contributor Jay Bolyard did an outstanding job describing how to make this repair.  — Rob, editor & chief floor sweeper.

This article describes how to replace the Smithy Granite 1324 Classic Combo Lathe-Mill-Drill’s ball bearings in its driven pulley.  The bearing may have to be replaced if it makes a noise like the one described below.

If….

  • Machine makes a bearing gone bad noise – you know it when you hear it – a zzZZzzZZzzZZ sound at low to medium speed – may not be able to distinguish the noise at higher speeds [Hear it in a .mp4 video]
  • The noise occurs in all three drive modes: lathe, mill and neutral (occurring in neutral is the key)
  • The noise occurs with and without the lead / feed gearing engaged
  •  The noise does not occur with the belt taken off
  •  The noise seems to come from the clutch and driven pulley area when machine is run with pulley box open

Then….

  • The ball bearing inside the driven pulley or the clutch bearing in the shifter fork (or both) are likely in distress and the source of the noise
  • They either need to be re-greased – or – since you’ve got it all apart – best to just replace them with permanently lubricated and shielded bearings

A few unique tools and a few supplies that are needed in completing this work

  • Large snap ring pliers – larger than most people have in their toolbox – must be capable of up to 4″ shaft – Like these found at Grainger Item 3JXL9 – Large Snap Ring Pliers at Grainger
  • Propane torch
  • 2-ft long 1/2″ threaded rod – with (3) matching hex nuts and (3) 1/2″ fender washers
  • Grease – I used Amsoil Multipurpose Synthetic Grease
  • Screwdrivers
  • Needle Nose Pliers
  • Wrenches
  • Rags
  • Parts schematics for reference
  • Access to an arbor or shop press – A mallet could be used if great care was taken – your decision
  • Approximately 5″ square and 2″ x 12″ pieces of wood – whatever is available – photos below show usage

Homemade or Hardware and Auto Parts store supplies

  • 2.33-2.45″ ID x ( 21/4″ long tube or equivalent tooling pre-made with lathe for use in pressing off the old and on the new clutch bearing.  (2″ Schedule 40 white PVC Drain Coupler – can be used instead – $1 at hardware store)
  • 2.8-3.1″ OD ( 1/4″ thick plate or 2.8-3.1″ OD tube ( 11/2″ long or equivalent tooling pre-made with lathe for use in pressing out the old pulley bearing.  (3″ ID to 3″ OD exhaust pipe adapter – can be used instead – $3 at auto parts store)
  • Two #8 x 1″ long machine screws (or pins ~ 5/32″ dia)
  • Two M5 x 0.8 bolts – at least 25mm long – easier if longer – suggest grinding/filing the tips smooth/flat to decrease face marking on the right coupler (G03-005)
  • 3.80-3.90″ OD ( 1/4″ thick plate or 3.75-3.90″ OD tube ( 1″ long or equivalent tooling pre-made with lathe for use in pressing in the new pulley bearing – I made it on a friends lathe because mine was already apart… (3″ grey PVC Electrical Coupler came close to working – needed to turn about 0.1″ dia. off 1/2″ of one end)

New Bearings

  •  1 – # 6011ZZ (2Z) – 55x90x18mm (Clutch Bearing). Minimum ABEC-3 with C3 clearance.  Choose ZZ (double shielded) vs. original open/open design to avoid need to periodically grease and keep contamination out of the bearing.  Cost depends on brand chosen – I chose Nachi-Japan.
  • 1 – # 6013ZZ (2Z) – 65x100x18mm (Pulley Bearing).  Minimum ABEC-3 with C3 clearance.  Again, choose ZZ (double shielded) vs. original single shielded design to avoid need to periodically grease and keep contamination out of the bearing.  Lack of good grease and the former machine owner keeping the belt tension engaged when not in use is likely what caused my bearing to fail.  Again – I chose Nachi-Japan. Continue reading Smithy Granite Clutch and Driven Pulley Bearing Replacement

Modifying a Craftsman 2 X 42-inch Belt Sander For Tool Grinding

The Craftsman 2 X 42-inch belt sander is a very good general purpose belt sander.  With its 1/2 HP motor it can handle most light duty work in the shop, including grinding lathe tools for both metal and wood lathes.  This grinder allows for very fast belt changes, tracks well with a simple adjustment and has enough power to grind tools without overheating or bogging down.  However, it does have two deficiencies that must be addressed before any serious grinding can be done on it — the main grinding table and the platen.

The OEM table is made of cast aluminum.  It pivots on and locks with a single large screw.  Firm pressure on the table can overcome this screw and the table will move with the belt running, which is very dangerous.  My advice is to dump it and build a decent table.

The OEM platen is stamped mild steel.  It is okay for light use like shaping Popsicle sticks but will not last long grinding lathe tools.  The platen is mounted solidly to the chassis and is fairly stiff but pressure on the belt will wear a divot into it quickly so basically it’s useless once this happens.

Resolving these deficiencies isn’t difficult but it requires some fabrication.  I’ll show you how I addressed them.

The Platen Fix

A grinder platen has to be solid and unyielding, flat and ideally long wearing despite driving a grinding belt and grit over its surface.  No steel platen I know of will withstand this kind of abuse for long but a ceramic glass liner will.  This liner is actually a high temperature glass material originally developed by Corning and is commonly sold by knife making suppliers in 2-inch wide X 1/4-inch thick slabs of varying lengths.  Commonly known as Pyroceram, it is usually mounted to a steel backing plate with JB Weld.  This stuff is highly wear and heat resistant and only a full-time knife maker is likely to ever wear one out.  If you do no other mods to your grinder at least do this one.

I used a 2-inch wide X 9-inch long X 1/4-inch thick piece of O-1 precision ground steel as a platen/backing plate because I wanted a flat mounting surface that would not move with heat over time.  I know that mild steel can move with localized heat and while this may not break the epoxy bond … it might.  So far, I have had no separation issues so this worked for me.

I drilled and tapped two 1/4-20 holes on each edge so the platen can be flipped over if the liner ever wears on one end.  A piece of 1/8-inch thick X 1.5-inch wide angle iron (not aluminum) is used to attach this backing piece to the side of the chassis using the OEM screws and platen mounting holes.  The mounting holes in the angle iron are slotted to allow squaring of the platen to the belt.  Offset your platen and chassis screws if you copy this; the way I did it works but it would be better if the screws were clear of each other.

Before attaching the liner to the platen, be sure to lightly bevel or round the side edges of the liner and more generously round the top and bottom edges to prevent cutting the belt.  This is best done on a slack 50-60 grit belt.  The sparks will be orange and the glass will glow but it grinds easily enough.  I also lightly sanded the side of the glass that would bed in epoxy using sandpaper overlying some plate glass to give the glass some tooth.

I put some oil on the tip of some 1/4-inch screws and use nuts to lock them down with their ends just flush with the epoxy side of the steel platen.  This is to keep the holes clear of epoxy.  After cleaning both contact surfaces with lacquer thinner, a 2 X 9 X 1/4-inch piece of Pyroceram is bedded onto the face of the platen with an even layer of JB Weld.  I covered the face of the glass with a thin piece of plywood and clamped it with 4 spring clamps and allowed it to dry for a full 24 hours.  JB Weld has the highest heat tolerance of any commonly available epoxy, at least to my knowledge.  Ideally, you want to have a ledge under the glass liner to keep it from being knocked loose but mine has been stable for many years without a ledge.  Be sure to use blue Loc-Tite to attach the platen to the grinder chassis so it won’t vibrate loose but can be easily removed if needed.

In use, the Pyroceram platen is used like any other platen.  Since it is glass you should avoid slamming hard objects into it but otherwise it is tougher than nails.  I have ground hardened steels, tools, and other assorted materials and have yet to see any indication of wear or movement over the years, though the picture shows some transfer of paint from the back of the belt.  Pyroceram is some truly amazing stuff.  The piece I used cost $20.00, delivered!

The Table Fix Continue reading Modifying a Craftsman 2 X 42-inch Belt Sander For Tool Grinding