Keyboard Shortcuts
Likes
Search
OT: Bainbridge 712 resurrection
|
I realize this is a bit off topic. However, I've recently come to own an old Bainbridge 712. While it isn't the best out there, the price was right and I couldn't pass it up. It is quite functional but the blade continues to jump off the wheels. After reviewing the archives, YouTube, etc and adjusting the heck out of all set screws, I believe some previous owner may have modified the saw past the point of adjustment. I've set up an indicator dial and the drive shaft runs rather true.? My question to the group. Does ANYONE know of someone with any knowledge on these saws? Perhaps even some pictures?? Any help would be greatly appreciated and reciprocated if I can. Thanks, Darren McCarley |
|
Hi Darren
Bainbridge made saws a lot like a 4x6.? I'm guessing a model 712 is a 7"x12".? If it is similar to their smaller ones, the same things that fix 4x6's will fix it.?? Please post a photo of yours so we can see. Will make it easier to give you advice.?? There's pics of a model 304 and a real old one in the File section of this site: (file:///C:/Users/vreed/Downloads/_Bainbridge%20band%20saw%20images%20Model%20_%20&%20Model%20304.pdf) They had washers for blade guides, not like anything modern which use ball bearings, but otherwise the way it works is the same. I'm sure we can help if you post a photo - jv |
|
John,
Thanks I have a couple of pictures. They are attached. As you can see, the drive shaft and wheel looks to have been modified. I can't confirm because I have nothing to compare against. I believe?the wallowed out hole used to be a set screw. But, I have found other capturing methods elsewhere on the saw. C-clip, dowel, etc.? I've taken a 3 foot rigid straight edge and run it from wheel to wheel. The result? The drive wheel is close. I've taken the upper adjustment screw and run it all the way in, all the way out, half way, etc and still the blade jumps with in just a couple of rotations. My initial thought? The drive wheel needs to sit closer to the end of the drive shaft. Drill new hole in the wheel hub, thread, and reuse a new set screw. Complete speculation though. Wheel pics with shaft protruding are of the drive wheel and shaft. The upper wheel and idler shaft are shown as well. Happy to take/post more pictures. Just let me know what you'd like to see. Any input is MORE than welcome. I'm no machinist. But I enjoy a good challenge, and take pride in bringing old tools back to life, and then using the hell out of them. :) thanks! Darren |
|
Forgot to say, pls include a photo of the tension guide block (the part that slides up and down to tension the blade, that the driven wheel axle is bolted to, taken from the back of the saw frame casting) as that shows the adjustment mechanism for tilting the driven wheel, and one of the way the drive wheel is fixed to the gearbox output shaft - jv
|
|
Great photos, exactly what we need.? I didn't see your photos until after my 2nd request.
The driven wheel axle tilting mechanism on yours is different to a 4x6. This is the main tracking device so you'll need to show me how the axle is tilted. Can you take off the driven wheel from its axle and photograph the tilting mechanism from the inside, maybe disassemble it and photograph too.? ? Tracking is straight-forward and I'll set it down for you while you get those additional photos.- jv |
|
Certainly. The upper wheel has the tilt adjustment. Too bolt and bottom in tilt combination then the center for set screw. Additional pics for context.? Shaft with dowel is the drive/lower. Shaft with the bearings is the tilt/upper Thank you! Darren
|
|
Welll, made some progress. I've been able to clean most of the moving bits and adjust the saw to the point where the blade runs with out coming off vertically and horizontally. However, as soon as I introduced a small bit of right angle steel, the blade falls off. The good thing is, the blade cut like hot knife like in butter! Less than 2 seconds and about 1/3" was cut. Bad thing about this? Now I REALLY want this working. :)?
Perhaps tighten the blade? Not sure how far to push the tightening. The blade does make a note when tightened. Not sure what note, but it? twangs. Any ideas? Thanks, Darren ps. If these types of updates are unwelcome, just let me know.? |
|
OK this is a long one:?
There are 3 adjustment that determine whether a blade will track on any bandsaw: 1.?? Blade tension 2.?? Driven wheel tilt 3.?? Drive wheel position on its axle ? It helps to understand why these things matter: Bimetal bandsaw blades are tensioned to 25-30,000psi stress, flexback carbon steel blades to 15-20,000psi.? That means a ?¡± wide bimetal blade, has about 300lb tension in it when tensioned properly. With a blade run on both sides of the wheels, that¡¯s 600lb force pulling the bandwheels together.? The sawframe casting flexes, any slack in bearings is pulled out, and axles and axle supports bend.? You can¡¯t set the tracking properly until you¡¯ve got the right tension in the blade.??It takes more than you think; on a 4x6 its about as much as a normal person can wind the 2?¡± diameter tension knob one handed, without any aids. It makes a real twang when plucked, not a dull thok.? Don¡¯t know what it will take on your 712, but if it¡¯s got a ?¡° blade, the tension will be half as much again as a ?¡± blade. ?You¡¯ll need to decide where full tension is, before you start tracking (see comments below on how to mark it) ? The drive lands on the wheels of metal cutting bandsaws are a (very short) parallel cylinder, not crowned like a wood bandsaw.? The blade is supposed to run not quite touching both rims. The rims are just there to make the blade easier to put on, not to track the blade. The drive and driven wheels and bearings are manufactured to be parallel to each other when there is no tilt in the driven wheel. ? However, when there is tension in the blade, the tension pulls the wheels out of parallel and the blade runs off. To counter this the driven wheel is tilted in at the top, which makes the blade track toward the rim on both wheels, more strongly at the driven wheel than on the drive wheel. ? Broadly speaking, you adjust the tilt so that the back of the blade runs about 1/32¡± (1mm) away from the rim of the driven wheel and allow the sawband to find its own place on the bottom rim, then move the bottom rim on its shaft in or out until the back edge of the blade just doesn¡¯t touch the rim on the drive wheel when the blade is at full tension. However there are a number of things to consider while doing this: 1. ??Tracking is tension dependent; the greater the tension the more the back edge of the blade moves away from the rim. 2.?? You can¡¯t change the tilt in the driven wheel without releasing the tension. 3.?? So, you must be able to re-tension the blade to the same value each time ¨C make a scratch with a scriber on one half of the tension mechanism and align the top edge of a piece of sticky tape with the scratch, stuck to the other half of the mechanism. It'll be different when you change blades as each is a slightly different loop length. 4.?? The roller blade guides do affect tracking a bit (will make it move in about 1/32¡± at top and 1/8¡± on bottom wheel, but its easier to track the blade without them in place ¨C so remove until you¡¯ve adjusted the blade to within 1/16¡± at top and 5/32¡± at bottom 5.?? The tracking is very sensitive to movement of the tilting set-screw. 1/6th turn changes it a lot near the correct point, less sensitive when just starting to tilt. 6.?? Start with set screw at ¡®no tilt¡¯ position (release blade tension, undo both bolts, back setscrew out, then tighten both bolts again, then turn setscrew back in until it touches). 7.?? It¡¯ll need at least ? turn in on set screw to start with so re-set the tilt with the set-screw half a turn in. 8.?? Tension blade so that the slack is just out of the blade, (i.e. no-where near full tension), and turn on/off quickly to see how the blade moves.? If it sits ok, then keep it running and slowly increase the blade tension and notice how it starts to move away from the rims. 9.?? If it still wants to move away from the driven wheel rim at less than full tension, increase the tilt another ? turn of the set screw each time, then 1/6th turn when you get near full tension, until the blade tracks ~1/16¡± from the rim of the driven wheel at full tension.? 10.? ?Don't worry about the drive wheel, unless it still derails even when the driven wheel tracks properly, that shows its way too far in on its shaft (N.B. see comment below about gearbox bearing failure) 11.?? Now move the driven wheel on its shaft until the back edge of the blade is ~5/32¡± from the rim 12.?? Re-install the roller blade guides and see if the blade tracks just clear (1/32¡±) of the rims.? Will be ok if it looks like its touching, but you can¡¯t hear any graunching noises (back edge of blade scraping hard on the rim). ? That¡¯s about it, though the blade must be welded squarely (watch for uneven gap from back of blade to rim as the join passes over the driven wheel) and the gearbox output shaft bearing must be ok (if it¡¯s failed the output shaft will bend as the tension is increased, so the blade derails from the bottom wheel only, not the top one).? You have to keep the blade on before you can judge either of these, so try to make it track as above first.? ? Don¡¯t be scared to move the drive wheel out, if it keeps derailing from the bottom when the top seems OK , though you do need to check that the gearbox output bearing hasn¡¯t failed? (they do it often enough and it could be the reason why it was sold). I see your drive wheel is pinned, 4x6¡¯s use a key and a set screw, you could use 243 Loctite until you get the position right, then re-pin it. ?243 Loctite is weak enough to be able to change the position of the drive wheel with heat and a gear puller to set the tracking, but even high strength Loctite won¡¯t be strong enough to drive when cutting metal.
Let us know how you get on - jv |
|
Of the top of my head, if it tracks ok but doesn't take downward pressure of cutting, most often the gap between the side roller guide bearings is too large.? Couple of schools of thought on this, one that they should have between zero and 4thou" clearance on the blade, the other that you should run 5-9thou" to allow swarf to run between blade and side roller. Anywhere in the range 0-9 thou" works.
Another possibility is that there is too much bow weight (weight of the sawframe casting when just held up above the cut with a weighing device (fishermans spring balance, or better and cheaper now, a $5 digital luggage weigh scale off eBay). Should be about 13lb on a 7x12 when the scale is hooked around the tension knob.? If much more than that can shuck the blade because it will be cutting too fast. - jv? |
|
JV, Fantastic feedback. Thank you! Funny how life works. I wouldn't have understood most of your explanation, if I hadn't worked through the challenges first. I greatly appreciate your time and sharing of knowledge. I'll attempt to respond in a semi-orderly fashion. Blade tension: I believe I'm still in the "thunk" area of tone. I'm right handed and will tension with my left till I get more of a "twang".? Wheels: These wheels seem to have a bit of crown and no rims (If I understand you). Perhaps a difference in desing? (Pics attached) Driven Wheel tilt: Thank you for the in depth explanation on how this works. I'll be modifying the saw to include a simple tension gauge/ruler. Drive wheel: The fact that this wheel is pinned continues to be a point of concern of mine. It looks like this wheel originally used a set screw. I assume the wheel was slipping on the shaft and someone stripped the threads trying to tighten the screw too much. In an effort to "fix" this mistake, perhaps they drilled and pinned the wheel. Thus negating ALL fore/aft adjustment of the drive wheel. I have a couple of options here. 1) Leave the pin. - HUGE assumption of accuracy and useability.? 2) Drill and tap 3 more holes and use 3 set screws 120¡ã off setting. I could go so far as to measure and flatten parts of the drive shaft to aid in anti-slip, but I REALLY do not want to modify beyond repair. (First, do no harm.) 3) Broach a keyway in the drive wheel and a LONG keyslot in the shaft. Ideal, but much more entailed than I THINK I need.?? * Your thoughts? Blade: The blade is a Lennox 3/4" blade Blade guides: The blade side guides are cammed. After a thorough cleaning, I re-installed them and I intentionally opened the gap as far as possible. I ignorantly assumed they may be causing the derailment. I'll readjust them.? * Am I correct in assuming the use of feeler gauges may be over kill here?? e.g. guide|blade|feeler gauge|guide Where the feeler guage = total clearance/2 Bow weight: EXCELLENT point on the Bow weight. I noticed the heft of the machine when lowering? the frame. I'll look into adjusting the spring. I never thought about using a luggage scale. I'll have to pick one of those up. As fast as the derail happens, and the amount of cutting that occurs just prior to that, I'd be willing to bet a combination of lack of roller guide support and weight is the culprit here. If that's the case, that is awesome. As it seems I'm quite close! Well, close to the next challenge anyway. :) More to come, and as always, thank you for your feedback! Darren
|
|
Nice to know you¡¯re making progress. Sorry my answers are a little long, but if you don¡¯t have enough info to understand why things work, you can¡¯t evaluate any how information meaningfully. To respond to your questions. ? Tension So far you¡¯ve only been interested in blade tracking, but once it tracks you¡¯ll need to make it cut straight and we get to another can of worms. ?If you read the doc in the files section called ¡®Bandsaw Chip Characteristics v3.pdf¡¯ you¡¯ll get the gist of what¡¯s happening as the blade cuts. The bits about ¡®weight on the tooth¡¯ and ¡®blade tension, stress and buckling¡¯ are important (the concepts, not the numbers which are different for your blade). ? Your blade is a ?¡± deep, 0.035¡± wide beam spanning 10 to 14¡± between the two back support rollers, (depending on how far apart your guides are), with the work pushing up roughly in the middle. In engineering terms it¡¯s a very slender beam; the only thing keeping it straight is its tension. The most important thing is that the blade cuts in the direction its pointing. When it buckles it no longer points straight down and it doesn¡¯t cut square down through the work. ?You need high enough tension and a low enough bow weight to stop it buckling, but not so high that the blade cracks and fails. ?Beyond that the actual tension doesn¡¯t matter very much.? ? You say you¡¯re still in the 'thunk' area, but be careful.? Your blade is longer and thicker than a 4x6 blade, both of which will make the tone lower. The tone it makes depends only on the span, the weight per unit length of the blade and the tension ¨C if you pluck the back run of the blade between the guide wheels and use a std blade then tension is the only?thing that changes the tone.? ? You¡¯d expect the bandsaw manufacturers to have given you a tensioning mechanism that you can use, without resorting to anything special, to tension it properly. ?Since you have to choose a repeatable tension to set the tracking, wind the tension knob as hard as you can with one hand and leave it at that. Use the scratch and sticky-tape marker method for this blade and record the tone on your cellphone¡¯s audio app to make it repeatable for other blades. ? I¡¯ve looked into all the methods of measuring tension I can think of, and there are no simple, cheap, ones where you know what the actual tension is. ? ? Wheel crown? Yes, your wheels are crowned.? That normally means the tilt is not so important as the blade will ¡®climb up¡¯ the crown when it runs.? Since it will climb up no matter which side of the wheel it¡¯s on, it should settle in the middle. You adjust the tilt to make the crown on both wheels the same, but the wheels need to vertically in the same plane, like 2 dishes lying on a flat table.? That makes the drive wheel position that much more important. If the rims are both the same thickness, you should be able to get it close with a long straight edge that lies across both wheels, touching at 2 points on both wheels.? A piece of extruded aluminium 1¡±x ? ¡° unequal length angle section, 1/16th¡± thick, cut to length to fit inside the saw frame casting is the best I¡¯ve found. Find it at most hardware stores. Extrusions are normally very straight in short lengths and the angle section stiffens it. ? ? Drive wheel Once you¡¯ve found the optimum position for the drive wheel it should not need to be moved again, so pinning it again is not a bad option, since you can do it with the minimum of tools.? 3 setscrews at 120deg is NOT a good option, as the whole load is concentrated at 3 points with the maximum amount of wiggle as it wears.? Wheel bosses are normally fixed to shafts with 2 set-screws at 90deg, though I¡¯ve seen an engineering paper where they said you get more friction between shaft and boss if they¡¯re spaced at 45deg! ?Flats for the setscrews to bear on are a must, though I¡¯ve no idea whether just 2 set-screws will be enough.? The boss on that drive wheel looks long enough to put in a double row of setscrews and I¡¯d be pretty confident that would be enough.? Broaching/cutting a keyway with a setscrew on top of the key is the preferred solution, if you can get it done cheaply enough. ? Blade guides Yes, feeler gauges are the right way. The blade is 0.035¡± so a set at 0.036¡± or 0.042¡± will do. The debate over clearance or no clearance is mainly about whether you cut steel or aluminium and/or use coolant.? Coolant and cutting aluminium both cause swarf to stick to the blade and get rolled through between the blade and the side guide rollers, so clearance is desirable. Steel swarf and in dry cutting the swarf falls away so only minimal clearance required which gives maximum blade direction control.? The best solution is to use minimum clearance and a blade scraper like in doc 'Liquid Coolant Lube on a 4x6 Bandsaw.pdf' in the Files section. ? Yeah, I think bow weight and side roller guide separation are your immediate problem too.? Happy hunting - jv |